Innate immunity:- Components: Neutrophils, macrophages, monocytes, dendritic cells, natural killer (NK) cells (lymphoid origin), complement, physical epithelial barriers, secreted enzymes.- Mechanism: Germline encoded- Resistance: Resistance persists through generations; does not change within organism's lifetime- Response to pathogens: Nonspecific, occurs rapidly (minutes to hours), no memory response- Secreted proteins: Lysozyme, complement, C-reactive protein (CRP), defensins- Key features in pathogen recognition: Toll-like receptors (TLR): pattern recognition receptors that recognize pathogen-associated molecular patterns (PAMPs) and lead to activation of NF-κB. Examples of PAMPs include LPS (gram ⊝ bacteria), flagellin (bacteria), nucleic acids (viruses).

Adaptive immunity:- Components: T cells, B cells, circulating antibodies- Mechanism: Variation through V(D)J recombination during lymphocyte development- Resistance: Microbial resistance not heritable- Response to pathogens: Highly specific, refined over time, develops over long periods; memory response is faster and more robust- Secreted proteins: Immunoglobulins- Key features in pathogen recognition: Memory cells: activated B and T cells; subsequent exposure to a previously encountered antigen → stronger, quicker immuen response.