Defense Date


Document Type


Degree Name

Doctor of Philosophy


Microbiology & Immunology

First Advisor

Shaun Ruddy


Purified human C3a was iodinated (125I-C3a) and used to study the interaction of labeled peptide with rat peritoneal mast cells (RMC). Cellular binding of 125I-C3a occurred within 30 sec, followed by a rapid dissociation from the cell. Both the binding of 125I-C3a and the rate of dissociation from the cell were temperature dependent. At 0°C, the binding of 125I-C3a was increased and the rate of dissociation reduced, as compared to 37°C. Once 125I-C3a was exposed to RMC, it lost the ability to rebind to a second batch of RMC. Analysis of the supernatants by trichloroacetic acid (TCA) precipitation and electrophoresis in sodium dodecyl sulfate polyacrylamide gels (SDS PAGE) revealed a decrease in the fraction of 125I precipitable by TCA and the appearance of 125I-C3a cleavage fragments. Pretreatment of RMC with enzyme inhibitors specific for chymotrypsin, but not trypsin, abrogated the degradation of 125I-C3a. Treatment of RMC bearing 125I-C3a with Bis (sulfosuccinimidyl) suberate (BS3) covalently crosslinked the 125I-C3a to chymase, the predominant enzyme found in the secretory granules. Antiserum directed against chymase precipitated 125I-C3a from extracts of RMC treated with BS3. Indirect immunofluorescence of RMC using the 1gG fraction of goat anti-rat chymase showed that chymase is present on the surface of unstimulated cells. Neither purified chymase nor heparin proteoglycan alone had any appreciable effect on 125I-C3a, but together they resulted in prompt degradation of the 125I-C3a. Immunoabsorption of RMC sonicates with specific antibody for chymase completely abrogated the ability of these sonicates to degrade 125I-C3a. Intact RMC were pretreated with serine esterase inhibitors prior to 125I-C3a and BS3 exposure. The cells to which 125I-C3a had been crosslinked to were solublized and analyzed by SDS PAGE and autoradiography. There were three bands visualized, a 35,000 dalton band which was defined as chymase, and two undefined 45,000 and 55,000 dalton bands. The results indicate that 125I-C3a binds to RMC and is promptly degraded by chymase in the presence of heparin proteoglycan. In addition, this proteolysis of 125I-C3a by chymase must be blocked in order to detect plasma membrane C3a binding components on RMC.


Scanned, with permission from the author, from the original print version, which resides in University Archives.


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