The Complement System 
it is perhaps no surprise that the body must keep 
it tightly regulated. Special proteins are synthe- 
sized to protect the body's own cells from dam- 
age by complement factors. Our laboratory dis- 
covered 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. Recently these 
regulatory proteins have been demonstrated to be 
expressed in relatively high concentrations on re- 
productive tissue, including placental tissue and 
sperm. A new direction for the laboratory con- 
cerns the role of these proteins in reproduction. 
Modulating the function of these regulatory pro- 
teins may also be important in improving means 
to kill tumor cells or in allowing xenografts to 
survive in humans. 
Because infectious, autoimmune, and immune 
complex-mediated illnesses result from aberra- 
tions of the complement system, our research ef- 
forts are helping to define the pathophysiologic 
basis of such diseases. In many autoimmune and 
immune complex-mediated diseases, there is an 
inherited defect in the handling of immune com- 
plexes or in the activation or regulation of the 
complement system. Variations in the structure, 
function, and expression of complement proteins 
are important aspects of autoimmune diseases. 
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