3.2
#69
MICA AND MICB ANTIBODIES IN PATIENTS WHO REJECTED KIDNEY TRANSPLANTS.
K. Mizutani , R. N.J. Shih , R. Pei , J. Lee , M. Ozawa and P. Terasaki . Los Angeles CA, USA, Terasaki Foundation Laboratory, 90064 and Canoga Park CA, USA, One Lambda,Inc., 91303 .

Although most kidney transplant patients who rejected a kidney have been shown to have HLA antibodies, some patients who reject did not have HLA antibodies. In order to see if these patients might have antibodies against the MICA and MICB systems, we tested those who had rejected their kidney grafts as well as patients who were transplanted and still had functioning grafts.
Our panel of test antigens was MICA*001,007,008 and MICB*002 prepared from an E. coli expression system as inclusion bodies or as membrane–bound proteins in a mammalian expression system. For E. coli expression, MICA or MICB cDNA's were modified by removing the coding sequences for signal peptides, transmembrane regions, and cytosolic tails.

Percent positive
NMICA1MICA7MICA8MICB
Normal subjects350002.9
Functioning transplantsWith HLA ab3414.78.805.9
Functioning transplantsNo HLA ab150000
Rejected graftsWith HLA ab4712.84.719.219.2
Rejected graftsNo HLA ab3520.017.18.611.4


The cut off values of the ELISA tests were set at 3x SD, at which point none of the 35 normal sera produced positive reactions for MICA. As noted above, among the patients with functioning transplants and HLA antibodies, some patients had MIC antibodies, but none of those without HLA antibodies could be shown to have MIC antibodies. Among the patients with rejected grafts, significantly, in 35 patients in whom we could not find HLA antibodies, MIC antibodies were found.
We conclude that antibodies to MIC are produced in the course of rejection of a kidney transplant. They may be as important as HLA antibodies in the ultimate rejection of the transplant. The panel of MIC antigens is now being expanded, and more extensive test results will be available.