Biology In Human Welfare Human Health And Disease 2

1. Immunity

• The body’s ability to defend against disease-causing organisms is called immunity.
• Immunity is crucial because we’re constantly exposed to infectious agents, yet only a few exposures lead to disease.
• There are two main types of immunity: innate and acquired.

2. Innate Immunity: Non-Specific Defenses

• Innate immunity is present from birth and provides non-specific defense.
• It comprises four types of barriers:
  • Physical barriers: Skin and mucus membranes (respiratory, gastrointestinal, urogenital tracts) trap microbes.
  • Physiological barriers: Stomach acid, saliva, and tears inhibit microbial growth.
  • Cellular barriers: Leukocytes (PMNLs, monocytes, natural killer cells, macrophages) phagocytose and destroy microbes.
  • Cytokine barriers: Interferons from virus-infected cells protect uninfected cells.

3. Acquired Immunity: Specific Defenses with Memory

• Acquired immunity is pathogen-specific and possesses memory.
• The first encounter with a pathogen elicits a primary response (low intensity).
• Subsequent encounters produce a stronger secondary (anamnestic) response due to immunological memory.
• This response involves B-lymphocytes and T-lymphocytes:

B-lymphocytes: Produce antibodies (proteins) that fight pathogens; antibody structure is H₂L₂. Examples of antibodies include IgA, IgM, IgE, and IgG. This antibody-mediated response is also called humoral immunity.

T-lymphocytes: Don’t secrete antibodies but assist B cells; mediate cell-mediated immunity (CMI), responsible for graft rejection.

4. Graft Rejection and Self vs. Non-self Recognition

• Organ transplantation requires tissue and blood group matching because the body differentiates “self” from “non-self.”
• CMI is responsible for graft rejection if there’s a mismatch. Immunosuppressants are often necessary after transplantation.

5. Active and Passive Immunity

Active immunity: The body produces its own antibodies in response to antigens (living or dead microbes, proteins). This is slow but long-lasting. Induced by infection or vaccination.

Passive immunity: Ready-made antibodies are given to the body. This is fast-acting but temporary. Examples include antibodies in mother’s milk (IgA) and those transferred across the placenta.

6. Vaccination and Immunization

• Vaccination is based on the immune system’s memory.
• Vaccines (antigenic proteins or weakened pathogens) stimulate antibody production and generate memory B and T cells.
• Passive immunization uses preformed antibodies (e.g., antitoxins for tetanus or snakebite).
• Recombinant DNA technology enables large-scale vaccine production (e.g., hepatitis B vaccine).

7. Allergies

• Allergies are exaggerated immune responses to environmental antigens (allergens).
• Allergens trigger the production of IgE antibodies.
• Symptoms include sneezing, watery eyes, runny nose, and difficulty breathing. Histamine and serotonin release cause these symptoms.
• Allergy testing identifies allergens, and antihistamines, adrenaline, and steroids treat allergic reactions. Modern lifestyles may contribute to increased allergy rates.

8. Autoimmunity

• Autoimmunity is when the body attacks its own cells due to genetic or unknown reasons.
• This results in autoimmune diseases, such as rheumatoid arthritis.

9. The Immune System: Organs and Cells

• The immune system includes lymphoid organs, tissues, cells, and molecules (antibodies).

Lymphoid organs: Primary lymphoid organs: Bone marrow (produces all blood cells) and thymus (T-lymphocyte maturation). Secondary lymphoid organs: Spleen (filters blood), lymph nodes (trap antigens), tonsils, Peyer’s patches (small intestine), appendix, and mucosa-associated lymphoid tissue (MALT) – a significant portion of the body’s lymphoid tissue. These organs facilitate lymphocyte interaction with antigens and effector cell proliferation.