Immune System

What are pathogens?

Pathogen: disease causing organisms 

What are infectious diseases?

 

• Infectious Disease: Disease caused by pathogens 

 

What are communicable diseases?

• Communicable/contagious disease: Infectious disease that can be passed from one person to another 

Bacteria

Bacteria 

• Most are harmless to humans 

  • Commensal/non-pathogenic 

  • Found everywhere including on skin, in gut 

• Some cause serious disease/death 

  • These are called pathogenic bacteria 

• Single cell organisms 

• Can be seen using a light microscope 

• Very small 

• Some can be prevented via vaccination 

• Some can be treated with antibiotics 

What are some diseases caused by bacteria?

Common Bacterial Diseases: 

• Tetanus 

• Salmonella 

• Whooping cough 

• Syphilis 

• Tuberculosis 

• Strep throat, ear infection 

• Golden Staph 

Virus

Viruses 

• Very small – can only be seen with electron microscope. 

• Contain genetic materials e.g. DNA/RNA, surrounded by protein coat. 

• Enter cell and use their DNA/RNA to take over cell processes so virus can reproduce. 

• Not all viruses are harmful/pathogenic - some are even used in biotechnology. 

• Cannot be treated with antibiotics. 

• Vaccines available for some deadly viral diseases. 

What are some diseases caused by viruses?

Common Virus Diseases: 

• Common Cold 

• Flu 

• Covid-19 

• Measles 

• Mumps 

• German Measles 

• Chicken Pox 

• Polio 

• Warts 

What are ways in which pathogens can be transferred?

• Contact

• Transfer of body fluids

• Droplet/Airborne Infection

• Ingestion

• Transmission by vector

• Vector = "carrier" 

• "vector" is another organism that carries the disease from one person to another 

What are the types of defences against diseases?

• External barriers - prevent entry of pathogens

• Protective reflexes - expel pathogens from body

• Non-specific defences - general response to a wide range of pathogens

• Specific defences/Immune response - responses to specific pathogens

What are some types of external barriers?

• Skin 

  • Effective barrier covering outside of body 

  • Stops entry of micro-organisms if unbroken 

  • Normal bacteria also provide protection – stop pathogenic bacteria from settling in. 

  • Secretes oily sebum – has substances that kill some bacteria 

  • Sweat can also prevent micro-organism growth 

 

• Mucous Membranes 

  • In mouth, nose, conjunctiva, reproductive tract 

  • Line body cavities that open to exterior 

  • Secrete mucus -  interferes with micro-organism entry 

 

• Hairs 

  • In nasal cavity, ears, eyelashes 

  • Trap pathogens for processing and removal 

  • Cilia – tiny hairs with beating motion – sweeps mucus and pathogens towards entrance 

  • Trachea 

  • Nasal cavity 

  • Other air passages 

 

• Acids 

  • Kill bacteria and other micro-organisms 

  • e.g. stomach acid, acidic vaginal secretions, sweat 

 

• Lysozyme 

  • Enzyme that kills bacteria 

  • Contained in tears, saliva, sweat, nasal secretions, tissue fluid 

 

• Cerumen 

  • Ear wax 

  • Slightly acidic, contains lysozyme 

  • Protects ear canal from infection 

 

• Flushing action of body fluids 

  • Helps keep free of pathogens 

What are some types of protective reflexes?

• Sneezing: 

  • Triggered by irritation of nasal cavity 

  • Expels dust, dirt, mucus, and pathogens from mouth 

 

• Coughing: 

  • Irritation of lower respiratory tract 

  • Air forced from lungs, taking mucus and pathogens up trachea and out 

 

• Vomiting: 

  • Contraction of muscles of abdomen and diaphragm 

  • Expels pathogens from stomach 

 

• Diarrhoea: 

  • Irritation of intestinal wall causes fluid to accumulate in intestines, plus explosive contractions of smooth muscle in intestinal wall. 

How can we assist the body’s external defences?

Assisting the Body's External Defences 

• Disease can be prevented by assisting the body in preventing pathogen entry. 

• Examples include: 

  • Wearing a mask to prevent spread of respiratory disease when you are sick 

  • Maintaining environmental hygiene 

  • Wearing condoms to prevent sexually transmitted diseases 

  • Mosquito nets to prevent mosquito-borne disease 

  • Frequent hand washing 

  • Sneezing and coughing into elbow 

  • Avoiding contact with people who are sick 

  • Self-isolating when unwell 

What are non-specific defences?

• Work against any pathogen that enters the body 

• Not specific to any one pathogen 

• Broad, generalised reaction to foreign substances or tissue damage. 

What are the different types of non-specific defences?

• Natural Killer Cells (NKC) 

• Phagocytosis 

• Inflammation 

• Fever 

• Lymphatic System 

What are NKC?

Natural Killer Cells (NKC) 

• A type of white blood cell (leucocyte) that kills everything they encounter by releasing chemicals 

  • Cytokines – alert and attract other immune cells 

  • Other chemicals that destroy cell membranes to kill unhealthy cells 

 

• Why don’t they kill healthy body cells? 

  • Healthy body cells have proteins on their surface that act "self" markers so they don’t get attacked 

  • Virus infected cells and cancer cells have fewer of these markers, so are more likely to be killed. 

What is phagocytosis?

 

Phagocytosis 

• Phagocytes: 

  • Cells that can engulf and digest micro-organisms and cell debris. 

  • Leucocytes (WBC) 

    • In blood stream 

    • Can leave blood and enter tissues at side of injury/disease 

  • Macrophages 

    • Some wander through tissue 

    • Some are fixed 

What is inflammation?

Inflammation 

• Response to any tissue damage 

  • Reduces spread of pathogens 

  • Removes damaged tissue and cell debris 

  • Begins repair of damaged tissue 

• Suffix of itis (refers to inflammation) 

  • Tonsilitis, laryngitis, meningitis etc 

• Four signs of inflammation: 

  • Redness 

  • Heat 

  • Swelling 

  • Pain 

What are the steps of inflammation?

Steps in the Process of Inflammation 

1. Tissue damage occurs 

• Pathogens may or may not be introduced to continue damage 

 

2. Tissue Damage causes Mast cells to release histamine and heparin 

• Histamine causes local capillaries to dilate and become leaky, allowing phagocytes and other leukocytes to enter the area. 

• This causes heat, redness, swelling and pain 

• Heparin prevents clotting in the immediate area 

 

3. Complement proteins are activated, and attract phagocytes 

• They are able to enter the area of damage due to the leaky, dilated capillaries from step b. 

• Phagocytes engulf and digest dead cells and bacteria 

 

4. Once pathogens are cleared, mast cells and complement stop messaging 

• Local capillaries return to normal 

• Phagocytosis ceases 

• Stage is set for tissue healing 

What is the process of fever?

• Part of the body's natural immune response to infection. 

• Body raises temperature to combat pathogens such as viruses or bacteria. 

• After encountering infection, WBC release pyrogens (fever causing chemicals) 

• Pyrogens affect the hypothalamus so that the normal set point of 37 temporarily reset to a higher temperature. 

• Hypothalamus then initiates warming responses to raise body temperature to the new, temporary set point 

• These include normal warming responses such as shivering, vasoconstriction, seeking warmth until the body temperature reaches the new "set point" 

• Once the infection has been dealt with the immune system stops producing pyrogens, and the "set point" returns to normal 

• The person then feels hot and cooling responses are activated 

• Fever is beneficial, but only up to a point. Prolonged, high fever can cause harm and even death, if the immune system is unable to deal with the infection quickly and effectively. 

What is the lymphatic system and what does it do?

The Lymphatic System 

• Network of vessels 

• Collect fluid in intracellular space, that has escaped capillaries 

• Moves it through a series of vessels (no pump – uses squeezing of skeletal muscles during body movement) 

• Lymph nodes filter lymph and trap pathogens 

• Returns it to blood circulation 

What do lymph nodes do?

Lymph Nodes 

• Filter lymph 

• Process cell debris, foreign particles, microorganisms 

• Contain lymphoid follicles that contain WBC (especially lymphocytes and macrophages) 

• Crisscrossed by fibers to trap particles 

• Can become swollen and inflamed during infection 

• Lymphocytes are also important in specific immunity 

 

What are specific defences against diseases?

Specific Defences against Disease 

• Tailored to each individual pathogen to overcome infection and to response quickly on subsequent encounters to clear infection before symptoms develop. 

 

• Creates "memory" to prevent getting it again 

What are the cells involved in specific immunity?

 

• Involves macrophages and other phagocytes 

  • Also involved in non-specific immunity 

  • Engulf pathogen and present antigen on surface to lymphocytes 

  • Are therefore "Antigen Presenting Cells" 

 

• Involves Lymphocytes 

  • Also involved in non-specific immunity 

  • Receive antigen and trigger specific immunity (cell-mediated and antibody-mediated) 

What are antigens?

• Antigens are substances capable of producing an immune response: 

  • The part of the pathogen that triggers the immune response: "antigenic site" 

 

• May not be a pathogen: Allergy occurs when the immune system reacts to a substance that is not harmful. Vaccines contain antigen to stimulate immunity without disease. 

 

• Usually large molecules 

 

• Could be a variety of things: 

  • Whole microorganism 

  • Part of the protein coat 

  • A toxin produced by a pathogen 

  • Foreign tissue (donor blood or tissue) 

What are antigen presenting cells (APC)?

• These cells are phagocytes, that ingest pathogens as part of the non-specific response. 

• They then present the antigen (part of the pathogen that the immune system recognises) on their surface. 

 

• They "present" the antigen to lymphocytes which are involved in the specific immune response. 

 

• Some examples of APC include: 

  • Macrophages 

  • Some lymphocytes 

  • Dendritic cells (not a focus in Y12 HB) 

What are lymphocytes?

• White Blood cells that are involved in both non-specific and specific defence. 

 

• Can be found: 

  • In blood circulation 

  • In tissues 

  • In lymph nodes 

 

• Produced in bone marrow 

What are the two different types of lymphocytes found in specific immunity?

• 2 Types involved in specific immunity: 

  • B-Lymphocytes (B-cells) - antibody mediated (humoral) immunity 

  • T-Lymphocytes (T-cells) - cell body mediated immunity 

  • Both produced by bone marrow, but mature in different ways 

What are the differences between B and T cells?

• B-cells 

  • Made in bone marrow 

  • Mature in bone marrow 

  • Move to lymphoid tissues and blood 

  • Involved in antibody-mediated (humoral) immunity 

 

• T-cells 

  • Made in bone marrow 

  • Mature in Thymus 

  • Move to lymphoid tissues and blood 

  • Involved in cell-mediated immunity 

 

• B and T cells make up the majority of the lymphoid tissues. 

How does specific immunity work?

APC and lymphocytes work together to identify and neutralise specific pathogens, and form memory cells so that long-term immunity to those pathogens is achieved. 

What are the two types of specific immunity?

• Antibody Mediated (humoral) - deals with pathogens before entry to cells 

• Cell Mediated Immunity – deals with pathogens that have entered cells 

What is the process of anti-body mediated immunity?

• Antibody-Mediated Immunity (Humoral Immunity) works against bacteria, toxins, and viruses before they enter the body’s cells; also against red blood cells of a different blood group other than the person 

 

1. Antigen-presenting cells recognise, engulf and digest pathogens, displaying the antigen on their surface. 

 

2. Antigen-presenting cells reach lymphoid tissue and present the antigen to lymphocytes. 

 

3. Help T-cells are stimulated by antigen-presenting cells, which release cytokinesis. 

 

4. Specific B-lymphocytes are stimulated to undergo rapid cell division. 

 

5. Most new B-cells develop into plasma cells, which produce antibodies and release them into blood and lymph. 

 

6. Antibodies combine with the specific antigen and inactivate or destroy it. 

 

7. Some of the new B-cells form memory cells. 

What is the process of cell-mediated immunity?

Works against transplanted tissues and organs, cancer cells and cells that have been infected by viruses or bacteria; also provides resistance to fungi and parasites.

1 Antigen-presenting cells recognize, engulf and digest pathogens, displaying the antigen on their surface.

2 Antigen-presenting cells reach lymphoid tissue and present the antigen to the lymphocyte.

3 Helper T-cells are stimulated by antigen presenting cells, which release cytokines.

4 Specific T-lymphocytes are stimulated to undergo rapid cell division.

5 Most new T-cells develop into killer T-cells or helper T-cells, which migrate to the site of the infection.

6 Killer T-cells destroy the antigen, while helper T-cells promote phagocytosis by macrophages.

7 Some sensitized T-cells form memory cells.

What are antibodies?

• A special type of protein with active sites/receptors that bind to specific antigen. Forms antigen-antibody complex. 

 

• Produced during antibody mediated immunity in response to non-self antigens. 

 

• Antibodies are also called immunoglobulins (Ig) 

What are the 5 different classes of antibodies?

• 5 Classes – IgA, IgD, IgE, IgG, IgM 

How do antibodies destroy pathogens?

• Antibodies surround pathogens and neutralise them in various ways by binding to their antigenic sites. 

What is the process of antibodies destroying pathogens?

• Specific antibody is produced in response to the specific antigen for a specific pathogen after it invades. 

 

• Antibody binds to the antigenic site on the pathogen, neutralising it in a variety of ways: 

 

1. Binding to active sites so virus/bacteria/toxin can no longer cause damage. 

 

2. Sticking multiple pathogens together – agglutination 

 

3. Reacting with soluble antigens to make them insoluble 

 

4. Inhibiting reactions in foreign cells or compounds, leading to cell breakdown 

Primary vs secondary response

Antibody concentration over multiple exposures to a specific pathogen 

• Primary response the first time a specific antigen is encountered. 

 

• Slower response – takes several days to clone B-cells and manufacture antibody 

 

• Symptoms occur and are then overcome 

 

• Secondary response: subsequent times that the specific antigen is encountered 

 

• Faster response – memory cells allow for faster recognition of antigen and therefore antibody release, before signs of illness develop. 

What is vaccination?

The artificial introduction of antigen to provoke antibody-mediated immunity to a pathogen without causing disease. 

Whats in the vaccine?

• Active ingredient – the antigen that causes the immune response. 

 

• Adjuvants – substances that assist the immune response to the antigen. 

 

• Stabilisers and Preservatives – stop the vaccine from deteriorating. 

 

• Antibiotics – prevent bacterial contamination during vaccine manufacture (only present in tiny amounts in the vaccine bottle). 

What are the 5 types of vaccines?

• Live Attenuated 

• Inactivated 

• Toxoid 

• Subunit 

• mRNA

What are live-attenuated vaccines?

Live Attenuated Vaccine 

• Vaccine made from live pathogens that are recognised by the immune system but are too weak to cause disease 

How are pathogens used in live-attenuated vaccines weakened?

How is the organism weakened? 

• Pathogen grown in a series of chick embryos in eggs. The pathogen replicates in one embryo, then is transferred to the next, in series. 

 

• As the series progresses, the pathogen becomes more adapted to chicken cells and less adapted to human cells. 

 

• By the end of the series, the pathogen is too weak to infect human cells but the human immune system can still recognise it. It takes around 10 years for the pathogen to become weakened. 

What are some examples of live-attenuated vaccines?

Examples of Live Attenuated Vaccines 

Bacteria	Virus
Tuberculosis (BCG)	Oral Polio Vaccine (OPV)  Measles, Mumps, Rubella  Rotavirus

What are inactivated vaccines?

 

Inactivated Vaccine 

• Vaccine made from killed pathogens that can't reproduce but can still be recognised by the immune system.

• Shorter length of protection than live attenuated, but can't revert back and cause disease 

How are pathogens used in inactivated vaccines killed?

• Killed using heat or chemicals 

What are some examples of inactivated vaccines?

Examples of Inactivated Vaccines 

Virus

Influenza (injected)  Pertussis (whooping cough)  Inactivated (acellular) Polio (injected)  Rabies

What are toxoid vaccines?

Toxoid Vaccine 

• For diseases where the pathogen causes disease by producing a toxin. 

 

• e.g. tetanus bacterium produces a neurotoxin that paralyses muscles, causing pain and death. 

 

• Created by inactivating the toxin so the antigenic site is still present, but the toxin no longer works, using heat or chemicals 

What are some examples of toxoid vaccines?

Examples of Toxoid Vaccines 

Bacteria

Tetanus  Diphtheria

What are subunit/conjugate vaccines?

Subunit and Conjugate Vaccine 

• Use only part of the pathogen to provoke the immune response 

• Can be done several ways 

  • Isolating the antigenic protein and just using that 

  • Using recombinant DNA technology to insert the antigenic protein into a harmless virus, or cells in culture so the antigen is presented/produced. 

What are some examples of subunit/conjugate vaccines?

Examples of Subunit Vaccines 

Virus

Human Papillomavirus  Hepatitis B  Some influenza vaccines  Some pertussis (whooping cough) vaccines

How can vaccines be delivered?

Vaccine Delivery 

• Commonly via injection 

  • Under skin 

  • Into muscle 

  • Not into bloodstream 

• Sometimes orally or via nasal spray 

  • "Flumist" 

  • Polio, Rotavirus 

• Current research into 

  • Incorporation into foods 

  • Skin patch 

What are booster vaccines/shots?

Vaccines and Boosters 

• Immunity decreases over time after vaccination. 

 

• The first response is quite short-term. 

 

• Two vaccines are often given within a short timeframe (usually a few months) to stimulate the primary and then secondary immune response. 

 

• Booster vaccines many need to be given much later as immunity decreases. 

 

• Some vaccines require boosters more often than others: 

  • Inactivated and toxoid vaccines need more frequent boosters 

  • e.g. whooping cough and tetanus vaccines 

What is the impact of vaccines on public health?

very good

What is herd immunity?

Herd immunity is the indirect protection from an infectious disease. Herd immunity occurs if enough people in a population are immune (whether it be through vaccination or immunity developed through previous infections) to a disease which protects the rest of the population by making the spread of the disease less likely.

• Protects people in the community who are unable to be vaccinated, or are immunosuppressed. 

• If enough people are in the population are vaccinated and immune, disease can't spread: the vaccinated people are a barrier or shield that prevents disease spreading through the community effectively. 

What are the 4 types of Specific Immunity?

Passive, Active, Natural and Artificial

What is Active Immunity?

Active

• Exposure to antigen causes body to actively produce immunity  ◦ Sensitation of lymphocytes, producing cell mediated and antibody mediated immunity  •   ◦ Memory cells    • e.g. When a virus naturally enters your body, your body actively fights it off via the process above.    • e.g. when you get a vaccine, your body actively produces antibody via the process above

What is Passive Immunity?

Passive

• Body gets "ready-made" antibody from another source – body does not need to actively work to produce the antibody. Body is not exposed to the antigen, so active immunity can't develop.    • Antibody received neutralises any pathogens present but will be used up    • No memory cells produced    • e.g. Antibody produced by the mother passes through the placenta and breast milk to the baby  • e.g. snake antivenom is bottled antibody that is injected into the blood to neutralise venom

What is Artificial Immunity?

Artificial

• Scientific processes are used to create immunity    • e.g. Vaccines are developed to produce active immunity without illness    • e.g. snake anti venom is produced so that antibodies to the venom can be injected into a person bitten by a snake to neutralise the venom

What is Natural Immunity?

Natural

• Immunity develops via natural processes in the human body    • e.g. When a virus naturally enters your body, your body actively fights it off via cell mediated and anti-body mediated immunity    • Antibody naturally produced by the body are passed from mother to baby via the placenta and breast milk so that the baby becomes temporarily, passively immune.

What is an example of Active Natural Immunity?

• Getting the measles 

 

• Measles is a virus that occurs naturally. 

 

• If someone is exposed to the measles virus, their immune system responds actively. 

  • B-cells and T-cells (lymphocytes) become sensitised. 

  • Produce antibody to fight the virus via humoral immunity. 

  • Produce memory cells specific to the virus so next encounter will be neutralised before symptoms develop. 

What is an example of Active Artificial Immunity?

• Receiving measles vaccine 

 

• The measles vaccine is artificial – it is man-made 

 

• A vaccine is given, containing either killed measles virus, substances that mimic the measles antigen, or a very mild form of the virus. The body then responds actively to produce long lasting immunity. 

  • B-cells become sensitised 

  • Antibody produced via antibody-mediated immunity 

  • Memory cells produced 

  • Immunity to measles results 

What is an example of Passive Natural Immunity?

• Child gets antibodies via breastfeeding or across placenta 

 

• The antibodies are made naturally by the mothers immune system 

 

• Baby gets antibodies from breastmilk or across placenta. The baby gets the antibody without the baby's immune system having to do anything. The process is passive. 

  • Baby then has circulating antibody to neutralise specific pathogen. 

  • Doesn't last – no active response from baby's immune system, no memory-cells produced. 

What is an example of Passive Artificial Immunity?

• Administration of snakebite anti-venom 

• Antibodies to snake venom produced via a man-made process (artificial) 

• Antibody injected into patient's blood stream: 

  • Antibody neutralises venom 

  • Body does not work to develop immunity – gets antibody passively 

  • Short term only – no memory cells produced 

What do booster vaccines do?

Booster shots remind the body’s immune system about the virus it needs to defend against. This improves/gives the immune system a boost. Booster shots of vaccines are often needed to utilize the secondary response to ensure that their is excessive/large levels of antibodies and memory cells to protect the body from disease.

What is the primary response after you’ve gotten vaccinated?

On the first exposure to an antigen the immune reaction is called the primary response. The boys immune system usually responds usually fairly slowly. Often taking several days to build large amounts of antibodies. This is because it takes time for the B-cells to multiply and differentiate into plasma cells and then secrete antibodies. Once the level of antibodies reaches peak. It begins to decline. However the primary response leaves the immune system with a memory of that particular antigen. 

What is the secondary response after you’ve gotten vaccinated?

With a second response or subsequent exposures to the same antigen the response is much faster due to memory cells recognising the antigen more quickly. With this secondary response, plasma cells are able to form very quickly, with antibody levels in the blood plasma rising rapidly to a higher level that last longer. This response is so quick that the antigen has little opportunity  to exert any noticeable effect on the body and no illness results.

What are antibiotics?

Antibiotics (antimicrobials) 

• Not the same thing as antibodies, antigens, or vaccines. 

• Anti - "against"  

• Biotics - "living things" 

• Class of drugs used to fight against micro-organisms – usually bacteria 

• Generally not preventative – they are given after infection to help kill the pathogen 

• Revolution in treatment of infection 

  • Before penicillin, many deaths resulted 

• Many classes of antibiotics, depending on mode of action 

  • Penicillin's: prevent bacteria from developing cell walls, therefore inhibiting reproduction 

  • Actinomycin's: interfere with protein synthesis in bacterial cells 

  • Cephalosporin's: interfere with bacterial cell wall synthesis 

What are the two broad types of antibiotics?

Two broad types: 

• Bacterial – kills bacteria by: 

  • Inhibiting cell wall synthesis 

  • Inhibiting bacterial enzymes 

  • Inhibiting protein translation within the bacterium 

• Bacteriostatic – prevent bacteria from multiplying while the immune system deals with them. 

  • Inhibit bacterial protein production 

  • Inhibiting bacterial DNA replication 

  • Interfering with other aspects of bacterial metabolism 

What are the different types of spectrum actions?

 

• Different spectrums of action: 

  • Broad spectrum 

    • Work against a wide range of bacterial types 

  • Narrow spectrum 

    • Effective against a narrow range 

 

• Each type of antibiotic only works against certain types of bacteria, even if broad spectrum. 

 

• Cultural and sensitivity is used to determine which bacterium is present and which antibiotic will work. 

  • Bacteria smeared on petri dish 

  • Discs with antibiotic put on 

  • Bacteria don't colonise areas with antibiotic that kill that bacterium 

 

• Antibiotics DO NOT work on viruses 

• Prescription from Dr required 

What is antibiotic resistance?

 

Antibiotic Resistance 

• Bacteria Evolve over time, to become resistant to antibiotics. 

 

• New antibiotics must be developed to combat this. 

 

• Things that contribute to resistance: 

  • Overuse of antibiotics, even when not necessary 

  • Agricultural use as 'growth promoters' in livestock 

  • Incorrect prescribing: giving an antibiotic that won't work, or as a preventative without good reason. 

 

• Some bacteria now show multiple drug resistance and total drug resistance, meaning we no longer have treatment for them. 

What are antivirals?

Antivirals 

• Specifically for viral infections. 

 

• Difficult to find drugs for this, as virus enters cell – any drug that interferes with virus may also harm host cell. 

   

• Antivirals inhibit development of virus, rather than killing it. 

  • "Zovirax" (acyclovir) - herpes 

  • Interferons – Hepatitis B 

  • AZT (azidothymidine) - HIV 

  • "Tamiflu" (Oseltamivir) - influenza 

What is the process of viral replication by HIV? 

1. HIV binds to the receptor site on T-lymphocyte 

2. Uncoated RNA from virus enters the lymphocyte 

3. The virus contains an enzyme that enables it to make a DNA copy of its RNA 

4. Host cell DNA in nucleus and DNA copy of HIV RNA integrates with host cell DNA 

5. New viral RNA produced 

6. Budding of new virus particle from lymphocyte 

7. New HIV able to infect other cells