Unusual Properties in Vitro and in Vivo of 198, an Antibody that Recognizes Rabbit Cd11b

Abstract

The leukocyte integrin CR3 (CD18/CD1lb) is thought to be important in the migration of neutrophils (N) into tissues during inflammation. The aim of the present study was to compare the properties of 6.5E, a mab with cross-reactivity against human and rabbit leukocyte integrin 13 chain CD18, with those of 198 and KIM 118, antibodies against the a chain of CR3 (CD1 lb) in rabbit and human cells, respectively. This was accomplished by assessing the ability of antibodies to block the adhesion of PMA-stimulated N (human N or glycogen elicited rabbit peritoneal N) to protein-coated plastic or to endothelial cells (from human umbilical vein (HUVEC) or rabbit ear (REEC) sources). In the human system, MM 118 and 6.5E were found to be potent at blocking adhesion of N to both plastic and HUVEC. IC₅₀ values for 6.5E and KIM 118 on plastic were 0.30 and 0.23 µg/ml, respectively; comparable values on HUVEC were 0.24 and 0.37 µg/ml. In the rabbit system, 6.5E also blocked adhesion of rabbit N to plastic and to REEC (IC₅₀ = 0.3 and 0.1 µg/ml, respectively); however whilst 198 blocked adhesion of N to plastic (IC₅₀ 1.0 µg/ml) it did not block adhesion of N to REEC. These results suggest that 198 recognizes an unusual epitope on CR3 or that LFA-1 and/or p150,95 are important regulators of adhesion in the rabbit. Data will also be presented to show the unusual effects of 6.5E and 198 in vivo