Immune response and vaccination
Phagocytes (neutrophils, macrophages) engulf pathogens; macrophages become antigen-presenting cells. T-helper cells with complementary receptors are activated and release cytokines. B cells with complementary receptors undergo clonal selection and expansion, forming plasma cells (secrete antibodies) and memory cells. Cytotoxic T cells kill infected cells. Antibodies: four polypeptide chains (2 heavy, 2 light), variable regions with two antigen-binding sites, held by disulfide bonds; cause agglutination, neutralisation and opsonisation. The secondary response is faster and larger because of memory cells. Active immunity (own antibodies; natural infection or vaccination) is long-lasting; passive (given antibodies; placenta, milk, injection) is short-term. Herd immunity protects the unvaccinated. Monoclonal antibodies target specific antigens for diagnosis and treatment.
≈ 50 min