The complement system is one of the most ancient immune defense mechanisms, providing rapid protection against invading micro-organisms. It is essential for the complement cascade to be under tight regulation in order to prevent excessive production of complement proteins. C5a is the most potent anaphylotoxin produced by the complement system, it binds C5a receptor (C5aR, CD88) and C5L2 (GPR77). C5a binding to C5aR induces leukocyte chemotaxis and release of inflammatory mediators. Over-production of C5a is known to be involved in many inflammatory and pathological conditions such as RA, I1R injury and sepsis, making it an attractive therapeutic target. Human and mouse C5aR share low homology and blocking C5a/C5aR signaling with small molecules has been challenging. We generated human C5aR knockout/knockin (hC5aR KI) mice in which the mouse C5aR coding region was replaced with that of human C5aR to utilize them for the development of human therapeutics targeting C5aR. hC5aR KI mice showed normal development, and leukocytes from hC5aR KI mice responded well to mouse C5a. We used two approaches to generate monoclonal antibodies (mAbs) against hC5aR. We used a mouse cell line transfected with hC5aR or neutrophils from hC5aR KI mice to immunize wild-type mice and generated high-affinity antagonistic mAbs which are specific to human C5aR. Anti-hC5aR mAb 7F3 blocked C5a-induced signaling completely without agonistic activity in vitro. In the animal model of K/BxN inflammatory arthritis, 7F3 both prevented and reversed inflammation. Currently, the function of the second C5a receptor, C5L2, remains controversial. There are contradicting reports from C5L2 KO mice that were generated by independent groups. We assessed the function of human C5L2 using an antagonistic mAb that specifically blocks C5L2 function and not C5aR. In vitro analysis using the C5L2-blocking mAb showed that C5a does not signal via C5L2 to affect chemotaxis or phagocytosis by neutrophils, indicating that C5L2 is not a signaling receptor for C5a, at least in these cellular functions.
| Identifer | oai:union.ndltd.org:ADTP/258412 |
| Date | January 2008 |
| Creators | Lee, Hyun, Clinical School - St Vincent's Hospital, Faculty of Medicine, UNSW |
| Publisher | Awarded by:University of New South Wales. Clinical School - St Vincent's Hospital |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Lee Hyun., http://unsworks.unsw.edu.au/copyright |
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