Genetic analysis of CR1 expression on erythrocytes of patients with systemic lupus erythematosus.

The role of genetic factors in decreased expression of CR1 in patients with systemic lupus erythematosus (SLE) was investigated by assessing the frequency of genotypes determining the numbers of CR1 on erythrocytes obtained from 52 patients with SLE and from 84 normal individuals. The expression of CR1 was quantitated using flow cytometry. Genotypes were determined by analyzing the CR1 gene restriction fragment length polymorphism using the CR1.1 complementary DNA probe and the Hind III restriction enzyme. In normal subjects, the distribution of the HH, HL, and LL genotypes fit the Hardy-Weinberg law. The frequency for the H allele did not differ between the 2 groups. No individual homozygous for the LL genotypes was found among the SLE patient population. Taken together, data from this and previous studies indicate an under-representation of the LL homozygous genotype in patients with SLE. SLE patients expressed decreased numbers of CR1 per erythrocyte within each genotype compared with these numbers in normal subjects. The results suggest that defective expression of CR1 in SLE patients is acquired and that the presence of the L allele is not linked to a genetic susceptibility for SLE.