|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.