The Complement System 
ruses and bacteria. As the circulating red blood 
cell passes through the liver or spleen, its im- 
mune cargo is released and metabolized. The red 
blood cell then returns to the circulation ready to 
ferry another load. 
Our laboratory is studying the complement re- 
ceptor involved in this process. We are also exam- 
ining the complement proteins that swarm onto 
the foreign particles. Furthermore, we are inves- 
tigating certain "housekeeping" proteins of the 
complement system. Because of the powerful de- 
structive capabilities of the complement system, 
it is perhaps no surprise that the body must keep 
this system tightly regulated. Special proteins are 
synthesized to protect the body's own cells from 
damage by complement factors. Our laboratory 
discovered a new family of genes that encode for 
at least six complement receptor and regulatory 
proteins. Two of these regulatory proteins occur 
on almost all cells of the body. These are termed 
decay-accelerating factor and membrane cofactor 
protein. Recently these regulatory proteins have 
been demonstrated to be expressed in relatively 
high concentration on reproductive tissue, in- 
cluding placental tissue and sperm. A new direc- 
tion for the laboratory concerns the role of these 
proteins in reproduction. Modulating the func- 
tion of these regulatory proteins may also be im- 
portant in improving the destruction of tumor 
cells. 
A further potential benefit from our research 
involves the field of transplantation. Presently 
the supply of donor organs is far less than the 
number of patients. Many people worldwide die 
while waiting for a suitable organ. Use of animal 
organs has not been possible, partly because of 
the complement system's attack on these trans- 
plants. However, this problem could be sur- 
mounted by using animal organs genetically engi- 
neered with complement regulatory proteins 
designed to prevent attack by the host's com- 
plement system. We are investigating these 
possibilities. 
Finally, because infectious, autoimmune, and 
immune complex-mediated illnesses result from 
aberrations of the complement system, our re- 
search efforts are helping to define the pathophys- 
iologic basis of such diseases. In many autoim- 
mune and immune complex-mediated diseases, 
there is an inherited defect in the handling of 
immune complexes or in the activation or regula- 
tion of the complement system. Variations in the 
structure, function, and expression of comple- 
ment proteins are important aspects of autoim- 
mune diseases. The information gleaned from 
such research efforts could provide a basis for 
new treatments. 
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