No quantitative relationship between CR1 and Lutheran expression on erythrocytes: In(Lu) gene product is not a common regulator of CR1 expression on erythrocytes.

The density of CR1, the C3b/C4b receptor (CD35), on erythrocytes (E) (CR1/E) is genetically determined. However, the broad distribution of CR1/E within a given genotype suggests that other genetic elements might contribute to the regulation of CR1/E. In some pathological conditions, including systemic lupus erythematosus (SLE), AIDS and hemolytic anemia, CR1 deficiency parallels the severity of the disease. When compared to healthy individuals, an accelerated decrease in CR1/E in these patients has been demonstrated, but other mechanisms interfering with CR1 density regulation during erythropoiesis might also contribute. In exceptional circumstances, CR1/E can be dramatically decreased in healthy individuals by the effect of a regulatory gene, In(Lu), that switches off various surface molecules on E, the structure genes of which are located on four different chromosomes, suggesting a transcription regulatory role for In(Lu) gene products. The hypothesis that products of this gene could physiologically regulate the surface density of all these molecules has been tested by determining Lub density on E (Lub/E) using quantitative flow cytometry. Lub antigenic sites were then compared to CR1/E among healthy individuals of the different CR1 density phenotypes, SLE patients with and without CR1 deficiency, and an exceptional SLE patient totally lacking CR1/E and reticulocytes. No quantitative relationship was found between CR1 and Lub expression in either normal or pathological conditions. These data establish that In(Lu) products are not involved in normal or pathological CR1 density regulation.

GIL: a red cell antigen of very high frequency.

A new high-frequency red cell antigen has been identified and named GIL. GIL differs from all high-frequency antigens included in the International Society of Blood Transfusion classification. There is very little family information and GIL has not been shown to be an inherited character. Five women with anti-GIL have been found. All had been pregnant at least twice. Red blood cells of two of the babies gave positive direct antiglobulin tests, but there were no clinical signs of hemolytic disease. Anti-GIL may have been responsible for a hemolytic transfusion reaction and results of monocyte monolayer assays of two of the anti-GIL suggested a potential to cause destruction of transfused GIL+ RBCs.