Human neutrophil structure and function with special reference to cytochrome b559 and beta 2-microglobulin.

ABSTRACT

Neutrophil granulocytes are the most important white blood cells in the combat of non-viral infections. Circumstantial evidence indicates that neutrophils in addition modulate the inflammatory process. Production of neutrophils takes place in the bone marrow, and mature cells egress to the circulation. Neutrophils emigrate following activation from the vessels into the tissues (chemotaxis). During this process neutrophils generate reactive oxygen species (respiratory burst) and mobilize intracellular compartments (degranulation). By degranulation, neutrophils exercise influence on nearby cells or bacteria by extracellular release of intragranular proteins (exocytosis), and intensify plasma membrane-related processes, such as chemotaxis and respiratory burst, by translocation of membrane-bound proteins to the surface (upregulation). Ultimately, microorganisms may be killed intracellularly following engulfment (phagocytosis). The thesis presents results of protein-chemical analysis of human neutrophils, based on studies of intact cells and subcellular structures (subcellular fractionation). By fractionation, azurophil granules and specific granules can be disunited from each other and from plasma membrane and secretory vesicles. Only partial separation of plasma membrane and secretory vesicles can be obtained. Subcellular structures are identified by markers, e.g. vitamin B12 binding protein for specific granules, and latent alkaline phosphatase for secretory vesicles. The studies demonstrated tetranectin in neutrophils, localized exclusively in the secretory vesicles. Tetranectin was released by incubation of neutrophils in the presence of weak, inflammatory stimuli and paralleled the upregulation of alkaline phosphatase, but preceded degranulation of specific granules. Alkaline phosphatase has previously been employed as a plasma membrane marker. A novel ELISA for HLA class I antigen was introduced as a new plasma membrane marker. Results obtained by this assay showed upregulation of alkaline phosphatase occurring without a concurrent redistribution of HLA antigen. This indicates that the two proteins are localized in separate compartments. Upregulation of alkaline phosphatase induced by weak stimuli, however, paralleled the translocation of cytochrome b559, anticipated to be the terminal component in the respiratory burst, and known to be localized primarily in the specific granules. The present studies indicate that 15% of cytochrome b is localized in the secretory vesicles. An ELISA was established for quantitation of beta 2-microglobulin, the light chain of HLA class I antigens. The concentration of beta 2-microglobulin in plasma from patients with chronic myeloid leukaemia was found to correlate with the concentration of vitamin B12 binding protein.4+ Measurements in neutrophils demonstrated 65% of the total content of beta 2-microglobulin to be localized in the specific granules, and 20% to be present in secretory vesicles.(ABSTRACT TRUNCATED AT 400 WORDS)