There are two distinct components of the
immune system, nonspecific and specific. Innate (natural) responses are
nonspecific, which act without precise antigenic recognitions of the target.

Innate immunity is present at birth and the defence mechanisms chosen are
encoded in the germline. Innate responses comprise of physiological barriers such
as skin, mucous membranes, temperature, pH and oxygen levels, phagocytic cells
(neutrophils, macrophages and monocytes), natural killer cells and cells that
produce inflammatory mediators (basophils, eosinophils, mast cells). Innate
responses also include soluble components like enzymes, antimicrobial peptides,
cytokines alongside complement and acute phase proteins. These components provide
first line of defence against antigens where pathogen- associated molecular
patterns (PAMPs) on the surface of pathogens are recognised by pattern
recognition receptors (PRRs) such as Toll-like receptors (TLRs) on the membrane,
NOD-like receptors in the cytoplasm, integrins, scavenger receptors and compliment
proteins in the circulation. This is followed by phagocytosis of the invading
microbes by monocytes circulating in the blood, phagocytes in tissues and
dendritic cells in tissues and lymphoid organs. Innate receptors identify
through multiple low-affinity binding and lack the molecular specificity
required for differentiating between non-selves. Innate responses also lack the
memory of antigens which contributes to the non-specificity. This imprecise
response can lead to destruction of surrounding tissues and organs 3,4,11.

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