An immunocytochemical study of the kallikrein-kinin system on the circulating neutrophil.
Inflammation is the normal biological response to tissue injury, and is characterised by the interactive activation of multiple mediators and cell types. One response to tissue injury is the production of pain, not only by direct trauma to sensory fibres, but also through the release of mediators from sensory nerve terminals. One such mediator is kinin which is a vasoactive peptide considered to play a primary role in inflammation by causing constriction of venules, dilation of arterioles, increasing permeability of the capillary membrane, and interacting with sensory nerve terminal transmitters to evoke pain. The kinin forming enzymes (kallikreins) reach inflammation sites either on the surface of migrating neutrophils or by transudation from plasma. The kininogen molecule which contains the kinin moiety, has been localised on the external surface of the neutrophil, and provides the substrate from which kinins can be cleaved through enzymatic action. The cellular actions of kinins are mediated through B2 receptors, which are also located on the external surface of the neutrophils. In addition, the induced effects of kinins are regulated by B1 receptors. The formation of nitric oxide (NO) from arginine released from the kinin C terminus, and receptor membrane signal transduction by nitric oxide following kinin receptor activation is discussed. A molecular response to cell injury is the formation of chemotactic mediators that attract neutrophils to sites of inflammation. The question whether neutrophils contribute to circulating levels of kinins was examined in infections and inflammatory disorders. This novel hypothesis was tested using circulating neutrophils harvested from patients with tuberculosis meningitis and pneumonia. These neutrophils showed a distinct loss of only the kinin moiety from the kininogen molecule located on the external surface. The confocal images of fixed, permeabilised neutrophils provided multi-dimensional constructs, and the intensity of fluorescence reflected the relative amounts of the molecule present in both neutrophils harvested from healthy volunteers as well as patient blood. The immunocytochemical labelling experiments using colloidal gold as markers, confirmed, at the ultrastructural level, the presence or disappearance of the kinin moiety from the kininogen molecule on the neutrophil surface. The cell component of synovial fluid in rheumatoid athritis (RA) consists mainly of neutrophils. This study demonstrates the absence of the kinin moiety from circulating and synovial fluid neutrophils from patients with RA, as well as an increased signal from immunolabelled B2 receptors in synovial fluid neutrophils. These findings support the hypothesis that in RA, kinins are released during the inflammatory response in the joints, and suggests that there is an upregulation of the B2 receptor at the site of inflammation. Neutrophils chemotactically drawn to the site of inflammation become activated to release kinin from the kininogen molecule, and thereafter re-enter the circulation where they were harvested systemically. B2 receptors may be upregulated following activation by kinins or by other mediators present in the inflammatory milieu. Interleukin-1 has been shown to upregulate kinin receptors on human synovial cells. Anti-peptide antibodies to the loops of cloned B1 and B2 receptors have provided powerful probes for the cellular identification of the two kinin receptor families. Mapping of the B2 receptors showed upregulation on the neutrophils gathered from inflamed joints. However, no activation of the Br receptors was observed in normal blood neutrophils as well as those obtained from the different disease states.