Extravascular T-cell recruitment requires initiation begun by Vα14+ NKT cells and B-1 B cells

Contact sensitivity and delayed hypersensitivity are principal in vivo models for recruitment of effector T cells into tissues. New data suggest that T-cell recruitment depends on an early antigen-specific ‘initiation process’. To begin, glycolipids released following skin immunization induce Vα14+ invariant natural killer T cells in the liver to produce interleukin-4, which, together with dispersed antigen, coactivates specific peritoneal B-1 B cells to produce circulating antigen-specific IgM antibodies within just one day. At elicitation, these antibodies form complexes with the antigen, thereby activating complement locally, generating C5a; this acts on local mast cells and platelets to release vasoactive serotonin and tumor necrosis factor-α, leading to T-cell recruitment. Similar ‘initiation processes’ probably mediate the recruitment of effector T cells in autoimmunity, asthma, infections and cancers.