Immunology - Innate & Adaptive Immunity Mechanisms

The body's first line of defense, providing immediate, non-specific protection against pathogens. It lacks immunological memory and includes physical barriers, phagocytic cells, natural killer (NK) cells, and the complement system.

Physical barriers (skin, mucous membranes), phagocytes (macrophages, neutrophils), natural killer (NK) cells, dendritic cells, mast cells, basophils, eosinophils, and the complement system.

PAMPs (Pathogen-Associated Molecular Patterns) are conserved microbial molecules (e.g., LPS, flagellin) recognized by innate immune cells. DAMPs (Danger-Associated Molecular Patterns) are host molecules released from damaged cells (e.g., ATP, uric acid) that signal tissue damage and inflammation.

A highly specific and diverse immune response that targets specific pathogens and develops immunological memory. It is mediated by lymphocytes (T cells and B cells) and takes time to develop but provides long-lasting protection.

1. Specificity: Targets specific antigens. 2. Diversity: Recognizes a vast array of antigens. 3. Memory: Remembers previous encounters for a faster, stronger secondary response. 4. Self-tolerance: Distinguishes self from non-self.

Cells that process and present antigens to T lymphocytes. Professional APCs include dendritic cells, macrophages, and B cells, which express MHC Class II molecules. All nucleated cells can present antigens via MHC Class I.

MHC Class I molecules are found on virtually all nucleated cells. They consist of an $\alpha$ chain and ${\beta }_2$-microglobulin. They present endogenous (intracellular) antigens, such as viral peptides or tumor antigens, to CD8+ cytotoxic T lymphocytes (CTLs).

MHC Class II molecules are primarily found on professional APCs (dendritic cells, macrophages, B cells). They consist of $\alpha$ and $\beta$ chains. They present exogenous (extracellular) antigens, such as bacterial proteins, to CD4+ helper T lymphocytes.