Inhibition of rejection of hamster-to-rat heart xenografts

Molecular isoforms of cobra venom factor-like proteins in the venom of Austrelaps superbus

Cobra venom factor (CVF) is characteristic of the elapid cobras and has not been reported from venoms of any other families of snakes. During our search for novel proteins, we isolated a polypeptide from the venom of the snake Austrelaps superbus (Lowland Copperhead) that showed structural similarity to C-terminal segment of the alpha-chain of CVF and hence named as AVFalphac (AVF-A. superbus venom factor). cDNA sequence of AVFalphac and its precursor indicated the presence of two isoforms of CVF-like proteins in A. superbus venom gland. This is the first report of molecular isoforms of CVF-like proteins in the venom of an Australian elapid snake. We have determined the complete cDNA sequence of both the isoforms (AVF-1 and AVF-2). They differ in their potential glycosylation sites and the characteristic thioester bond sequence. They display the overall domain structure of CVF and complement C3 proteins. By real-time quantitative analysis, we show that there is a 140-fold difference in the mRNA expression levels of the two isoforms in the venom gland of A. superbus. We also show the presence of AVF-1 and its variant (not AVF-2) in A. superbus venom by partial purification, dot blots, Western blots and peptide mapping using mass spectrometry. Partially purified proteins activate human Factor B in the presence of Factor D and Mg(2+), and deplete the complement activity in human and guinea pig serum. The bimolecular complex (AVFBb) formed activates complement C3 but not complement C5. Thus, AVF proteins may serve as potential candidates for therapeutic complement depletion without side effects. Thus, the discovery of CVF-like proteins in the venom of this Australian elapid snake provides an alternative source of research tools, and contributes to our understanding of the structure-function relationships and evolution of new members of CVF-like proteins.

T cell response in xenorecognition and xenografts: a review

Xenotransplantation has recently become a subject of interest for the transplantation community due to the current organ shortage, which could be partially or even totally solved by the development of this strategy. The humoral response, which arises as a result of species disparities, is the major obstacle to the success of xenotransplantation. However, if the use of different strategies such as plasmapheresis, immunoadsorption, the utilization of organs from transgenic pigs for complement regulatory molecules and new immunosuppressive drugs, may allow to overcome or reduce the early antibody mediated rejections (hyperacute or acute vascular rejection), delayed responses based on cellular activations will still occur. In this review, despite the fact that different cell populations have been shown to be implicated in these phenomena (NK, granulocytes, macrophages), we will focus on recent published information concerning T cell response only, in xenorecognition.

Evidence for a primarily humoral rejection mechanism in concordant xenogeneic heart transplantation. A sequential immunohistological study in a hamster-to-rat model

Heterotopic heart transplantations in an unmodified hamster-to-rat model were studied sequentially by immunohistochemical analysis. Monoclonal mouse anti-rat antibodies against B cells, T cells, macrophages and neutrophilic granulocytes (MRC OX-19, MRC OX-38, MRC OX-8, MRC OX-22, MRC OX-33, MRC OX-41 and MRC OX-42) were used in an indirect immunoperoxidase technique and monoclonal mouse anti-rat IgM and IgG were used for immunofluorescence. In grafts investigated after 6 h (N = 8) minimal infiltration of macrophages was demonstrated with MRC OX-41+ and MRC OX-42+ cells. No T- or B cells were seen. In a few cases, deposition of IgG and IgM was seen related to the endothelium of larger vessels. In grafts examined 24 h after transplantation (N = 10) the number of MRC OX-41+ and MRC OX-42+ cells had increased and in half of the cases IgM and IgG were located in relation to endothelial cells of larger vessels. In grafts investigated 48 h after transplantation (N = 8) the infiltration with MRC OX-41+ and MRC OX-42+ cells had further increased and a few scattered MRC OX-19+ and MRC OX-8+ cells appeared. At this time all but one heart had deposition of IgG and IgM in the vessel walls. Upon complete rejection (N = 8) diffuse infiltration of MRC OX-41+ and MRC OX-42+ cells was seen, but still only a few scattered T cells could be demonstrated. At this time IgG an IgM deposition appeared in all vessels and was also located in relation to the capillaries. These results further support our hypothesis that acute xenograft rejection in this animal model is primarily of the humoral type.