Defense against disease part 1

pathogen

disease-causing microorganism (virus, bacteria, protozoa, fungus, protozoan parasites, helminthic parasites, etc.)

bacteria

• nucleoid, no nucleus

• prokaryotes

• divide by binary fission (asexual)

• cell walls composed of peptidoglycan

• infectious and non-infectious

• food poisoning, salmonella, conjunctivitis, strep throat, cholera, etc.

viruses

• DNA or RNA (single stranded or double stranded), no nucleus

• require host cell to reproduce

• cannot be killed by antibiotics

• flu, common cold, HIV, herpes, etc.

fungi

• have nucleus

• eukaryotes

• polysaccharide chitin in cell walls

• reproduce by producing spores

• athlete’s foot, skin rashes, vaginal candidiasis, allergic reactions, ringworm, etc.

protozoan parasites

• parasitic or symbiotic organisms

• unicellular eukaryotes → treatment difficult

• Malaria, Leishmaniosis, Giardia, Trypanosoma, Sleeping sickness, Lyme disease, etc.

helminthic parasites

• parasitic diseases

• multicellular and eukaryotic

• elephantiasis, schistosomiasis, toxocariasis, pinworm, roundworm, tapeworm

prion

protein molecules which enter the body and reach brain tissue where more proteins are converted to prion proteins, causing brain cell malfunction and disease

innate immune system

responds to broad categories of pathogens, does not change during an organism’s life

• skin and sebaceous glands

• mucous membrane

• phagocytes

skin

much of the body is covered by tough layer of dead cells containing large amounts of protein keratin, physical barrier to entry of pathogens and physical or chemical damage

sebaceous glands

associated with hair follicles on skin, secrete chemical sebum, maintaining skin moisture and slightly lowering skin pH to inhibit growth of bacteria and fungi

mucous membrane

thinner and softer type of skin secreting mucus, found in areas such as the vagina, foreskin, head of penis, and airways leading to the lungs

mucus

sticky solution of glycoproteins

• physical barrier trapping harmful particles and pathogens to be swallowed or expelled

• antiseptic properties because presence of anti-bacterial enzyme lysozyme

blood clotting

cascade of events triggered by blood platelets and clotting factors, reduces chances of invasion by disease-causing organisms

1. skin is cut blood vessels are severed and start to bleed

2. platelets/blood-cell fragments aggregate at site of damage to blood vessel

3. platelets form a temporary plug and release clotting factors to trigger clotting process

4. clotting factors initiate cascade of reactions, resulting in production of enzyme thrombin

5. thrombin converts protein fibrinogen dissolved in blood plasma to insoluble fibrin

6. fibrin forms a mesh in cuts, trapping more platelets and blood cells

7. resulting gel clot which dries to form hard scab if exposed to air

phagocytes

type of white blood cell

• which squeeze out through pores in walls of capillaries and move to site of infection

• engulf pathogens by endocytosis, digest pathogens using enzymes from lysosomes

• large number attracted to infected wound results in formation of white liquid pus

macrophage

specialized phagocytes which kill extracellular pathogens and display antigens on plasma membrane

adaptive immune system

responds in a specific way to particular pathogens using memory of encountered pathogens, offering more effective protection against common infectious diseases, includes antibody-producing lymphocytes

lymphocytes

antibody-producing cells circulating in blood and occurring in large numbers at lymph nodes the lymphatic system, have a rounded nucleus and a small amount of cytoplasm

• each can produce only one type of antibody, small number for producing each type of antibody

antibody production

1. macrophage ingests pathogen and displays antigens from it

2. helper T-lymphocyte specific to the antigen is activated by the macrophage

3. B-lymphocyte specific to the antigen is activated by proteins from the helper T-lymphocyte

4. B-lymphocyte divides repeatedly to produce antibody-secreting plasma B-cells

5. antibodies produced by the clone of plasma B-cells are specific to antigens on the pathogen and help to destroy

antigen

glycoprotein (sometimes other proteins or large polysaccharides) located on the surface of the pathogen which stimulates an immune response by triggering lymphocytes to produce antibodies

• occur on cancer cells, parasites, bacteria, pollen grains, viruses, cells from another human

2. helper T-lymphocyte specific to antigen is activated by the macrophage

antibody-like receptor protein on plasma membrane of specific helper T-lymphocyte binds to antigens displayed by macrophage

major histocompatibility complex (MHC) proteins

protein complexes which present antigens and help cells of the immune system identify one another

• coded for by a group of genes on chromosome 6, genetically specific and unique to each individual

3. B-lymphocyte specific to the antigen is activated by proteins from the helper T-lymphocyte

helper T-lymphocyte activates B-lymphocytes by binding antigen to B-cell’s specific receptor protein and releasing signaling protein

4. B-lymphocyte divides repeatedly to produce antibody-secreting plasma B-cells

• B-lymphocytes do not immediately produce antibody upon activation because they lack necessary organelles and there are too few B-lymphocytes to make significant quantities of antibody

• activated B-lymphocytes divide repeatedly by mitosis to form a clone of cells that all produce the same antibody

• B-lymphocytes grow in size and differentiate into plasma B-cells (or memory B-cells)

plasma B-cells

cells that have grown and differentiated for antibody production

• extensive endoplasmic reticulum with many ribosomes attached

• large Golgi apparatus

5. antibodies produced by the clone of plasma B-cells are specific to antigens on the pathogen and help to destroy

structure of plasma B-cells allows for rapid production of antibodies by protein synthesis

antibodies

large proteins that help destroy pathogens with two functional parts

• hypervariable region that recognizes and binds to a specific molecule on a pathogen

• region that helps body fight the pathogen

antibody-antigen binding

• lymphocyte produce antibodies in response to antigen

• hypervariable region of antibody binds to antigen based on matching shapes (protrusions match hollows) and chemical properties (positive matches negative)

• irreversible

• does not cause antigen to change chemically

• antibody hypervariable region causes specificity in binding

immunity

ability to eliminate an infectious disease from the body, caused by either antibodies against pathogen or memory cells that allow rapid production of antibody

short-term immunity

• antibodies persist in body for a few weeks or months after secretion by plasma B-cells

• plasma B-cells that secrete antibodies gradually lost after infection overcome due to absence of associated antigens

long-term immunity

• most B-cells in a clone produced by mitosis become active plasma B-cells, the rest become memory B-cells

• plasma B-cells do not survive long after fulfilling role of rapid antibody production

• memory B-cells do not immediately secrete antibodies and remain for a long time after infection

memory B-cells

inactive until activated by infection of same specific pathogen and allow rapid production of antibody

human immunodeficiency virus (HIV)

retrovirus which uses reverse transcriptase to convert its RNA genome into DNA, which is subsequently integrated into host DNA, cause of AIDS

• invades and destroys helper T-lymphocytes, causing progressive loss of capacity to produce antibodies

• immune system weakened as a result, fewer antibodies are produced, diseases develop easily

transmission of HIV through bodily fluids

may be present in blood, semen, vaginal fluids, rectal secretions, and breast milk

• sex without a condom, during which abrasions to the mucous membranes can cause minor bleeding

• sharing of hypodermic needles by intravenous drug users

• transfusion of infected blood, or blood products such as factor VII

• childbirth and breastfeeding

early stages of HIV infection

positive test if immune system’s antibodies against HIV are detected

late stages of HIV infection

• antibody production becomes so ineffective that a group of opportunistic infections can strike

• pathogens which are normally fought off easily by healthy immune system are used as marker diseases (e.g. Kaposi’s sarcoma)

acquired immune deficiency syndrome (AIDS)

collection of several diseases or conditions existing together acquired after HIV infection once CD4+/helper T-lymphocytes cells drop below a critical level and the immune system is ineffective, leaving patients susceptible to opportunistic infections

HIV treatment

• antiretroviral drugs inhibiting reverse transcriptase

• drugs targeting enzymes that insert viral DNA into host cell’s chromosomes or prepare coat proteins for assembly of new virus particles

• groups of antiretroviral drugs slow down or prevent damage to the immune system

antibiotic

chemical that inhibits growth of microorganisms by disrupting metabolism of prokaryotic cells without affecting eukaryotic cells

• target bacterial DNA replication, transcription, translation, ribosome function, cell wall formation

antibiotic resistance

bacteria experience selective pressure when antibiotics kill susceptible bacteria and leave behind resistant bacteria which survive and reproduce, occurs as a result of

• spontaneous DNA mutation

• obtaining genes encoding antibiotic resistance (transformation, conjugation, transduction)

Methicillin-resistant Staphylococcus aureus (MRSA)

bacteria responsible for infections of blood or surgical wounds of hospital patients, shows increasing rate of resistance

measures to avoid antibiotic resistance

• doctors prescribing antibiotics only for serious bacterial infections

• patients completing courses of antibiotics

• hospital staff maintaining high standards of hygiene to prevent cross infection

• farmers not using antibiotics in animal feeds to stimulate growth

• introduction of new types of antibiotics

antibiotics as incompatible for blocking processes in eukaryotic cells

viruses use host cell metabolism to reproduce and therefore cannot be targeted by antibiotics

antiviral drugs

• some target specific proteins

• many target specific stage of viral life cycle

• interferons stimulate immune system to prevent replication of invading virus