MONITORING OF ANTI-HLA ANTIBODIES BY LYMPHOCYTOTOXICITY AND SOLUBILIZED
HLA CLASS I
ANTIGEN ELISA.
R Wassmuth, M-L Arnold, C Baum, JR Kalden. Institute
for Clinicical Immunology, University of Erlangen-Nürnberg, Erlangen,
Germany.
HLA class I-directed IgG antibodies have classically been
detected by complement-dependent lymphocytotoxcity (CDC). More recently,
ELISA-based methods using either lymphocyte-derived soluble class I antigens
or solubilized, platelet-derived class I molecules have become available.
Thus, the aim of the present study was to evaluate the solubilized HLA
class I antigen ELISA (QuikScreen, GTI, Brookfield, WI, USA) and standard
CDC testing (Lymphoscreen, Biotest, Dreieich, Germany) in a comparative
fashion. A total of 607 samples were drawn from the quartely antibody
screening of a total of 675 patients awaiting kidney transplantation. The
crosstable analysis indicated a concordant result in 510 cases (-/- 510;
+/+ 52 cases) while descrepancies were seen in 54 cases. In 11 patients
the CDC was positive while the ELISA tested negative. On the contrary,
34 patients had a positive ELISA and and a negative CDC result. Using McNemar's
test, this heterogeneity was statistically significant (c2=10.8; p=0.001).
In two patients IgM antibodies were identified causing a primary positive
CDC testing result. In six other patients the sera tested also negative
using the soluble HLA-based PRA-STAT test (SangStat, Menlo Park, CA, USA).
The remaining three sera were characterized by the presence of both class
I and class II-specific anti-HLA antibodies. From the pool of 34 CDC-negative,
ELISA-positive patients, 15 out of 16 sera available tested negative. When
the PRA values and the absorbance-derived ELISA-percentage (EP = SA*100/PC)
were compared, no significant correlation was seen. Considering CDC testing
the gold standard, the QuikScreen ELISA predicted a negative test result
with a sensitivity of 93.8% and a specificity of 82.5%. It is concluded,
that the solublized, platelet-derived class I-specific ELISA adequately
predicts a negative CDC test result and may thus be used to screen previously
CDC-negative patients without a history of intercurrent immunzing events.