RELATIONSHIP OF ANTICARDIOLIPIN ANTIBODIES AND ANTIPHOSPHOLIPID SYNDROME TO HLA-DR7 IN MEXICAN PATIENTS WITH SYSTEMIC LUPUS-ERYTHEMATOSUS (SLE)

We studied IgG and IgM anticardiolipin antibodies (aCL) by an ELISA me thod in 80 Mexican systemic lupus erythematosus (SLE) patients and 378 of their first degree relatives. Sixty five percent of SLE patients a nd 16% of their relatives were positive for aCL. We also determined al lele and haplotype frequencies of Major Histocompatibility Complex (MH C) genes (classes I, II and III) in both patients and relatives. MHC a llele and haplotype frequencies of aCL positive and negative individua ls were compared to those of normal ethnically matched controls. SLE p atients with aCL had statistically significant increased corrected fre quencies of HLA-DR3 (pC=0.04, RR=2.78); DR7 (pC=0.005), RR=3.42) and D Q2 (pC=0.003, RR=2.58) antigens. Their first degree relatives positive for aCL also had increased frequency of HLA-DR7 but it did not remain significant after correcting the P value. On the other hand, SLE pati ents negative for aCL had a moderate increased frequency of DR3 and DQ 2 but not of DR7. These results suggest that DR7 associates with the p resence of aCL. The distribution of MHC alleles in SLE patients positi ve for aCL resembles that found in their aCL positive first degree rel atives. Since the presence of the antibody is not sufficient to predic t a clinical outcome, we studied those patients with reliable clinical data regarding the presence of the antiphospholipid syndrome (aPLS). SLE patients with aPLS had significantly increased frequency of DR7 (p C=0.004), as did those with probable aPLS (pC=0.05), while the frequen cy of DR7 in SLE patients in the doubtful or negative aPLS categories was no different from normal controls. These data support a possible r ole of DR7 in the development of aCL in SLE patients and their relativ es and suggest a contribution of this class II MHC antigen to the deve lopment of aPLS within SLE.