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# Immune System Components **Opsonins** * Substances present in serum that promote phagocytosis of bacteria (act as markers). * Examples: IgG antibody, C3b molecule of the complement system. **Opsonize** * The ability of antibodies and complement components (and other proteins) to coat harmful a...

# Immune System Components **Opsonins** * Substances present in serum that promote phagocytosis of bacteria (act as markers). * Examples: IgG antibody, C3b molecule of the complement system. **Opsonize** * The ability of antibodies and complement components (and other proteins) to coat harmful antigens. * This allows the antigens to be recognized by antibodies or complement receptors on phagocytic cells. Opsonins act like tags for recognition by the immune system. **Phagocytosis** * A process where certain living cells (phagocytes) engulf and digest other cells or particles. * Example: Neutrophil phagocytosing a bacterium. **Apoptosis** * A type of programmed cell death in which a series of molecular steps lead to the death of a cell. * This is a method the body uses to eliminate unnecessary or abnormal cells. * Apoptosis can be blocked in cancer cells. **Antigen-Presenting Cell (APC)** * Cells that process protein antigens into peptides. * These peptides can then be presented to T-cell receptors on the cell surface. * Examples: Macrophages, dendritic cells, and B cells. **Complement System** * Part of the innate immune response involved in host defence and inflammation. * Plays a crucial role in the immune response. * Three different pathways for activation: * Classical pathway * Alternative pathway