The CBF.78 monoclonal antibody to human sialophorin has distinct properties giving new insights into the CD43 marker and its activation pathway

We confirm here the CD43 specificity of the CBF.78 monoclonal antibody (mAb ) and compare its phenotypic and functional capacities to classical group-A mAbs (DFT1, MEM-59) and to 2 other CD43 mAbs (RDP/AD9, 161-46). It reacts with stable human CD43 transfectants in a sialic acid independent way and b locks completely cell binding of RDP/ADS or 161-46 more or less but not DFT 1 and MEM-59. Its distribution differs from all other CD43. B lymphocytes, but surprisingly the majority of granulocytes or monocytes are CBF.78 negat ive. CBF.78 is expressed on all T lymphocytes, but the number of CBF.78 mol ecules/cell is low and equally represented on resting T CD4 and CD8 cells. In comparison to naive T lymphocytes, CD45RO cells increase their CBF.78 ep itopes much more than other CD43 epitopes. At a single cell level, confocal microscopy shows that CBF.78 can exist independently of other epitopes. CB F.78 is able to induce homotypic adhesion in different cell lines but not i n peripheral blood lymphocytes and is unable to relocalise the targeted mol ecules. U937 cell line that is not agglutinated by CBF.78 (or RDP/ADS) unde rgoes a stronger adhesion with PMA when this reagent is combined with this mAb. By itself CBF.78 is unable to activate T lymphocytes and to costimulat e CD3 mAbs but partially blocks PMA. The phosphorylation of the tyrosine ki nase p59(fyn) and p56(lck), driven by CBF.78, is weak and almost blocked by PMA. Altogether these data support the hypothesis that there are at least 3 modes of interaction between PKC and CD43 pathways: each pathway is inhib itory towards the other but the CD43 one can also be synergistic.