Practice question

Vaccines function primarily by inducing immunological memory mimicking natural infection without causing severe pathology. Upon antigen administration intramuscularly or mucosally, local dendritic cells and macrophages sense danger signals via pattern recognition receptors TLR, NLR, STING. Activated dendritic cells pick up antigen, mature upregulating CCR7, migrate to draining lymph node T cell zone presenting peptides on MHC class II to naive CD4 T cells and via cross presentation on MHC I to CD8 cells. T follicular helper cells provide IL-21 and CD40L signals to B cells in germinal centers driving proliferation, somatic hypermutation of immunoglobulin variable genes mediated by AID, affinity maturation, class switch recombination to IgG and IgA isotypes, generation of long lived plasma cells homing to bone marrow secreting high affinity antibodies years, and memory B cells expressing surface Ig capable of rapid differentiation upon rechallenge. Memory CD4 and CD8 T cells persist as central memory and tissue resident populations secreting IFN gamma, IL-2. Upon natural exposure, anamnestic response within 2-3 days neutralizes pathogen preventing disease. Adjuvants enhance this process.