Immune System — Key English Terminology

1.Innate immunity is fast (minutes to hours), nonspecific, has no memory. Components: skin barriers, mucosa, phagocytes, NK cells, complement, inflammation. Receptors: pattern recognition receptors PRRs, like TLR.

2.Adaptive immunity is slow (days), highly specific, has memory cells. Components: T cells, B cells, antibodies. Receptors: B cell receptor BCR and T cell receptor TCR.

3.Helper T cell, T-helper, marker CD4: secretes cytokines to activate other immune cells. Without CD4 helpers, B cells cannot do class switching and cytotoxic T cells are not fully activated. HIV attacks CD4 T cells leading to AIDS.

4.Cytotoxic T cell, T-cytotoxic, marker CD8: directly kills infected cells using perforin and granzyme. Regulatory T cell, marker CD4 plus CD25: suppresses immune response and prevents autoimmunity. Memory T cell: faster and stronger secondary response.

5.IgG: monomer, most abundant — about seventy-five percent. Only Ig that crosses the placenta. Functions: neutralization, opsonization, complement activation. Mnemonic: G equals greatest amount.

6.IgA: dimer, about fifteen percent. Mucosal immunity — saliva, breast milk, intestinal secretions. Mnemonic: A equals mucosal Area.

7.IgM: pentamer, about ten percent. First to appear in primary immune response; strongest complement activation. Mnemonic: M equals first Made.

8.IgE: trace amount. Allergic reactions via mast cell degranulation; also anti-parasitic. IgD: trace, B cell surface receptor; function not fully understood.

9.Year one fourteen exam point: after vaccination, primary response mainly produces IgM, secondary booster response mainly produces IgG — abundant, high affinity, long-lasting.

10.Clonal selection theory four steps: One, diversity generation via V(D)J recombination — each B and T cell has a unique receptor. Two, antigen selection — antigen binds the best-matching receptor. Three, clonal expansion — selected cells proliferate. Four, effector and memory differentiation.

11.Core concept: the immune system does NOT create matching receptors upon encountering antigen. Instead, millions of receptors already exist in advance — one per lymphocyte — and antigen merely SELECTS and expands the matching clone.

12.Active natural: recovery after infection — memory cells, long-lasting. Active artificial: vaccination — memory cells, long-lasting. Passive natural: maternal IgG crossing the placenta — no memory, temporary. Passive artificial: antibody injection or antiserum — no memory, temporary.