| Innate immunity | Adaptive immunity | |
| COMPONENTS | Neutrophils, macrophages, monocytes, dendritic cells, mast cells, eosinophils, basophils, natural killer (NK) cells (lymphoid origin), complement, physical epithelial barriers, secreted enzymes. | T cells, B cells, circulating antibodies |
| MECHANISM | Germline encoded | Variation through V(D)J recombination during lymphocyte development in the bone marrow |
| RESISTANCE | Resistance persists through generations; does not change within an organism’s lifetime | Microbial resistance not heritable |
| RESPONSE TO PATHOGENS | Nonspecific
Occurs rapidly (minutes to hours) No memory response |
Highly specific, refined over time Develops over long periods; memory response is faster and more robust |
| SECRETED PROTEINS | Lysozyme, complement, C-reactive protein (CRP), defensins | Immunoglobulins |
| KEY FEATURES IN PATHOGEN RECOGNITION | Toll-like receptors (TLRs) on macrophages and dendritic cells: pattern recognition receptors that recognize pathogen-associated molecular patterns (PAMPs) and lead to activation of the transcription factor NF-κB → activates immune response genes → immune mediators.
Examples of PAMPs include LPS (on outer membrane of gram ⊝ bacteria) recognition by CD14 on macrophages, flagellin (bacteria), nucleic acids (viruses). Dectin-1 pattern recognition receptors on phagocytes detect fungi. |
Memory cells: activated B and T cells; subsequent exposure to a previously encountered antigen → stronger, quicker immune response
TLRs are also present.
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