A NOVEL MONOCLONAL-ANTIBODY MNI-58A AGAINST THE ALPHA-CHAIN OF LEUKOCYTE FUNCTION-ASSOCIATED ANTIGEN-1 (LFA-1) BLOCKS THE HOMOTYPIC CELL-AGGREGATION AND ACTIVELY REGULATES MORPHOLOGICAL-CHANGES IN THE PHORBOL-MYRISTATE ACETATE (PMA)-ACTIVATED HUMAN MONOCYTE-LIKE CELL-LINE, U937

A monoclonal antibody (mAb), designated mNI-58A, was produced by immun izing mice with the lipopolysaccharide (LPS)-stimulated monocyte-like cell line, U937. The antigen defined by mNI-58A was widely expressed o n various lymphoid cells and all cell lines examined except the erythr oid cell line, K562. When the reactive patterns between mNI-58A and th e mAbs to various human differentiation antigens (CD11a, CD11b, CD11c, CD14, CD16, CD18, CD23, CD28, CD29, CD31, CD43, CD44, CD45RA, CD50, C D54, CD58, CD80, CD102, CD106, HLA-class I and -class II antigen) were compared, that of mNI-58A was found to be similar to those of the leu kocyte function-associated antigen-1 (LFA-1) mAbs. Using a competitive immunofluorescence binding assay it was found that the preincubation with one of the CD11a mAbs, 2F12 completely blocked the subsequent bin ding of mNI-58A. mNI-58A prevented the homotypic cell aggregation of t he phorbol myristate acetate (PMA)-activated U937 cells (referred to a s PMA-U937) and PMA-activated Epstein-Barr virus (EBV)-transformed B c ell lines, B-85 and Mann. mNI-58A markedly induced the spread formatio n of the PMA-U937 cells following this blocking of the homotypic cell aggregation, whereas 2F12 did not under the same condition. The spread formation induced by mNI-58A was completely blocked by cytochalasin B (CyB), cytochalasin D (CyD), cycloheximide (CHX) or protein kinase C inhibitors, sphingosine and H-7. The U937 cells markedly adhered to th e tumor necrosis factor-alpha (TNF-alpha)-stimulated human umbilical v ein endothelial cells (HUVECs) and also to the extracellular matrix pr otein, fibronectin, but mNI-58A did not enhance or block these adhesio n processes. mNI-58A precipitated two glycoproteins with molecular wei ght 180 kDa and 95 kDa as determined by SDS-PAGE analysis, which were identical to the LFA-alpha (CD11a) and beta (CD18) chains of leukocyte integrin precipitated by the CD11a mAbs, respectively. Sequential imm unoprecipitation studies using the CD11a mAb (2F12) also indicate that mNI-58A recognizes an epitope on the alpha-chain of the LFA-1 molecul e. The ability of mNI-58A to block the PMA-U937 cells and to induce th e spread formation of these cells suggests that mNI-58A is a novel mAb reacting with an epitope on the alpha-chain of LFA-1 different from t hose recognized with the existing CD11a mAbs.