Table 1.

Immune system components used for assessing the effects of social status on immune function.

immune component	description	examples	references
innate (non-specific)	host defences that exist before antigen exposure; generally confers non-specific and constitutive immune defences although inducible and specific properties are critical in certain innate defences. Three main defences are: phagocytosis, inflammation and the complement cascade	macrophages, neutrophils, basophils, eosinophils, natural killer (NK) cells and antimicrobial peptides/proteins (complement, defensins, c-reactive proteins)	[62,63]
adaptive (specific)	host defences that are mediated by antigen exposure and the activation of B and T cells. Adaptive components of the immune system exhibit highly diverse specificity to pathogens, retention of immunological memory and non-self-recognition	B lymphocytes, T lymphocytes, T helper cells, T cytotoxic cells, antibodies	[62,64]
constitutive	components of either the innate or adaptive arm of immunity that are expressed at all times; a non-induced form of immune function; confers a first line of defence against pathogens prior to pathogen-specific antigen exposure	examples of constitutive innate components: marcrophages, heterophils, granulocytes, NK cells and various antimicrobial peptides/proteins examples of constitutive adaptive components: naturally circulating antibodies (e.g. IgM)	[31,57,58,65,66]
inducible	components of either the innate or adaptive arm of immunity that are expressed following challenge by a pathogen; innate components induce inflammatory responses and increase rates of immune responses; adaptive components induce immunological memory, opsonization of pathogens and cell-mediated responses	examples of inducible innate components: production of reactive oxygen species (ROS) and cytokines by macrophages and granulocytes examples of inducible adaptive components: B lymphocytes, T helper cells, antibodies	[31,57,58]
Th-1 mediated	subset of adaptive immunity; secretes a unique profile of cytokines; Th-1 cells provide cellular immunity against intracellular bacteria, protozoa, fungi and viruses, help to eradicate cancer cells and stimulate delayed-type hypersensitivity (DTH) inflammatory reactions; important for macrophage and cytoxic T-cell activation	acute phase responses; cytokines including IFN-γ, TNF-α, TNF-β, TGF-β	[51,67–70]
Th-2 mediated	subset of adaptive immunity; secretes a unique profile of cytokines; Th-2 cells provide humoral immunity against helminths and other extracellular pathogens; stimulates B cell, eosinophil and mast cell production and is subsequently important in the upregulation of antibody formation; induces B-cell class switching	antibody production; cytokines including IL-4, IL-5, IL-6, IL-10 and IL-13	[51,67–70]