Pathologic quiz case 2. Benign capillary hemangioma.
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Ear Canal↗
Biomedical subjects
R A Krueger
Publications and source records attributed to R A Krueger.
Amidation of C3 at the thiolester site: stimulation of chemiluminescence and phagocytosis by a new inflammatory mediator.
We studied the ability of particle-bound and fluid-phase C3b monomers and monomeric amidated C3 (prepared by treatment of purified human C3 with ammonium chloride or methylamine) to stimulate chemiluminescence of human polymorphonuclear leukocytes (PMN) and monocytes and to promote phagocytosis in the absence of antibody. Particle-bound C3b evoked chemiluminescence from both PMN and monocytes, and fluid-phase C3b (0.5 mg/ml) elicited significant chemiluminescence from PMN but not from monocytes. Amidated forms of C3, both particle bound and fluid phase, were potent stimulators of chemiluminescence from phagocytic cells and caused a significantly greater response than did C3b. The phagocytosis of 1-micron microspheres by PMN and monocytes was enhanced by coating them with purified C3b in an antibody-free system. Microspheres coated with amidated C3 were avidly phagocytized, and to a greater degree than were C3b-coated microspheres. In a direct binding assay with tritiated monomeric C3b and amidated C3, the affinity of the PMN complement receptor type 1 for C3b (Ka = 4.9 X 10(7) L/M) was similar to that for amidated C3 (Ka = 5.7 X 10(7) L/M). However, there was a fourfold increase in the number of apparent binding sites for amidated C3. This increase did not reflect binding of amidated C3 to the complement receptor type 3, because blocking of CR3 with the monoclonal antibody OKM 10 failed to decrease binding of amidated C3. In sites of increased ammoniagenesis, such as the kidney in chronic renal failure, amidated C3 may play a role as an inflammatory mediator by stimulating oxidative metabolism in phagocytic cells.
Ammonium Chloride↗
The biochemistry of opsonization: central role of the reactive thiolester of the third component of complement.
In these studies, we have defined the mechanism by which the opsonic fragment of the third component of complement (C3) binds to pathogenic bacteria. With use of purified human C3 to reconstitute the alternative pathway in human serum in which both C3 and C4 had been chemically inactivated, we showed that opsonization of pathogenic serotypes of Streptococcus pneumoniae (serotypes 3, 4, 6A, 14, and 18C) requires the reactive thiolester of native C3. When purified human C3 (thiolester intact) is added to serum deficient in C3 and C4, phagocytic uptake of 3H-labeled pneumococci by polymorphonuclear leukocytes from normal adults is fully reconstituted. However, hydrolysis of the thiolester or reaction of the thiolester with the inhibitor methylamine abolishes opsonization and phagocytosis. Finally, by characterizing those C3 fragments released from pneumococcal surfaces after treatment with 1.0 M hydroxylamine, we have defined a role for covalent-bond formation in the opsonic interaction. Therefore, the presence of the reactive thiolester of C3 is an absolute requirement for the opsonic and covalent binding of the C3b molecule to pathogenic bacteria.
Chemical Phenomena↗