topic 8 pt 2 - immunity

1. Distinguish between the general characteristics of innate immunity and adaptive immunity.

2. Describe the all components of innate immunity, including physical barriers, chemical mediators and cellular defences.

3. Describe the all components of adaptive immunity, including antibody-mediated and cell-mediated immunity.

innate (non specific)

all foreign matter attacked equally

• forms body’s first and second line of defence

• contains physical barriers, chemical mediators, and cellular responses.

adaptive (specific)

describes the body's ability to recognise and respond to specific foreign substances and involves lymphocytes known as B-cells and T-cells. Adaptive immunity not only responds to specific substances, but also remembers them so that it can respond more efficiently should they be encountered again.

first line of defence

• physical and chemical - skin and muscous membranes

examples:

• The acidic pH of skin secretions (called the acid mantle) and usually of urine (pH of 4.5 to 6) inhibits bacterial growth, and sebum contains chemicals that are toxic to bacteria. The vaginal secretions of adult females are also very acidic.

• Sticky mucus traps many microorganisms that enter digestive and respiratory passageways.

• The stomach mucosa secretes gastric juice containing hydrochloric acid and protein-digesting enzymes that both kill pathogens.

• Saliva and lacrimal secretions (tears) contain lysozyme, an enzyme that destroys bacteria.

second line of defence

• natural killer cells - roam body in lymph and blood, lyse (burst) foreign substances by attackin membrane and releasing perforin and enzymes, which degrade cell content

• inflammation, redness, pain, heat, swelling

• fever, white blood cells release pyrogens which reset body thermostat/temp set by hypothalamus to a higher temperature.

antigen

An antigen is any substance capable of provoking an immune response. Foreign antigens are large, complex molecules that are not normally present in our bodies. Consequently, they are foreign intruders, or non-self. An almost limitless variety of substances can act as antigens, including virtually all foreign proteins, nucleic acids, many large carbohydrates, and some lipids. Pollen grains and microorganisms such as bacteria, fungi, and virus particles are also antigenic.

specificity

• Specificity means the adaptive immune system can target a particular antigen.

• B cells and T cells have surface receptors that recognise specific parts of an antigen based on their shape and chemical structure.

• B cells can bind antigens directly. Once activated, they can become plasma cells that produce antibodies specific to that antigen.

• T cells recognise antigen fragments displayed on other cells. They help coordinate the immune response or kill infected cells.

lymphocytes

• Lymphocytes provide specific immunity by recognising particular antigens and responding to them.

• Some kill infected or foreign cells directly. Others release chemical signals that activate immune cells or increase inflammation.

• Lymphocytes circulate from the blood → tissues → lymph → blood, allowing them to detect antigens throughout the body.

adaptive immunity

• Adaptive immunity consists of four types of cells: three classes of lymphocytes, called B lymphocytes (B cells), T lymphocytes (T cells), and natural killer cells, and a class of non-antibody producing cells, called antigen presentation cells (APC). Adaptive immunity can be divided into two main processes: antibody-mediated immunity and cell-mediated immunity.

antibody mediated immunity

• Antibody-mediated (humoral) immunity targets pathogens in extracellular fluids, including blood and lymph.

• Activated B cells multiply and develop into plasma cells, which produce antibodies, and memory B cells.

• Clonal selection activates lymphocytes whose receptors match a particular antigen.

• Primary response occurs on first exposure. Antibody production is slower, with IgM appearing first, followed by IgG.

• Secondary response occurs on repeat exposure. Memory cells produce a faster, stronger and more effective response, particularly involving IgG.

• The secondary response may prevent symptoms from developing.

• Antibodies are also called immunoglobulins (Igs).

cell mediated immunity

• Cell-mediated immunity is controlled by T cells and targets infected or abnormal body cells.

• T cells recognise antigen fragments presented with MHC proteins on cell surfaces.

• Activated T cells multiply to form clones of effector and memory cells.

• Cytotoxic T cells directly kill virus-infected, cancerous and foreign transplant cells.

• Helper T cells activate other immune cells, including B cells, promoting antibody production.

• Regulatory T cells suppress immune activity and help stop the response once the threat is removed.

• Memory T cells remain long-term, allowing a faster response to the same antigen.

• Cell-mediated and antibody-mediated immunity often work together.

active immunity

• when b cells encounter antigens and produce antibodies against them in your own body.

• can be naturally aquired or artificially through vaccines (dead or attentuated)

passive immunity

individual receives ready-made antibodies from an external source rather than producing them through their own immune system.

• Natural Passive Immunity occurs when maternal antibodies are transferred to a fetus through the placenta during pregnancy or to an infant via breast milk (particularly colostrum) after birth.

• Artificial Passive Immunity is induced through medical interventions, such as the injection of immune globulins (pooled from human donors) or antivenoms (derived from animals like horses) to provide rapid defense against specific pathogens or toxins.