Production and characterization of a unique monoclonal antibody against human B cells (33.2.1)

A new monoclonal antibody recognizing a linear determinant on the HLA-DRalpha chain N-terminus

We report the generation of a monoclonal antibody (MAb) that reacts to the N-terminus of the denatured HLA-DRalpha chain. The 1C4.6 MAb was raised against a peptide corresponding to amino acid residues 10 to 32 of a highly conserved region within the alpha1 domain of HLA-DR. This region partially overlaps with the epitope recognized by the conformationally dependent L243 MAb. In Western blot analysis, MAb 1C4.6 reacted with denatured HLA-DRalpha chains, but failed to bind the HLA-DRbeta chain expressed individually by transfectant cells, confirming that it recognizes an epitope on the alpha-chain of HLA-DR. In addition, this antibody was found to be isotype specific to HLA-DRalpha, as it did not cross-react to HLA class II proteins HLA-DP and-HLA-DQ. The 1C4.6 MAb is a valuable addition to existing reagents used to probe the structure and function of MHC class II molecules. This anti-HLA-DRalpha1 domain MAb may prove valuable for studies of HLA class II heterodimer assembly, structure, and function, as well as for studies into the release of soluble MHC class II.

Anti-HLA-class II monoclonal antibodies inhibit polyclonal B cell differentiation in vitro at the accessory cell level

We produced and characterized a panel of anti-HLA class II monoclonal antibodies (mAb) to study the inhibition of T cell-dependent B cell differentiation. The newly produced mAb belonged to different isotypes and subclasses, and recognized at least two different nonpolymorphic HLA class II determinants. We found that anti-HLA class II mAb inhibited the pokeweed mitogen (PWM)- and interleukin 2-driven T cell-dependent IgM synthesis, but did not affect the phorbol myristate acetate-, phytohemagglutinin-, anti-T3- or PWM-induced T cell proliferation. Moreover, when the mAb were tested in a monocyte-independent B cell differentiation assay in which T cells are activated by insoluble anti-T3 mAb in the absence of accessory cells, no effect was seen on IgM synthesis. These data indicate that inhibition of T cell-dependent B cell differentiation by anti-HLA class II mAb is caused by interference with an accessory cell function essential for B cell differentiation.

Studies of the pathogenesis of angioimmunoblastic lymphadenopathy

We studied the immune functions of two patients with angioimmunoblastic lymphadenopathy (AILD) in an attempt to determine whether the B cells were primarily hyperactive or, rather, if T cell abnormalities might underlie the B cell hyperactivity observed in these patients. We found that the B cells of the AILD patients did not proliferate spontaneously, nor were they induced to proliferate excessively by fresh normal T cells. In contrast, AILD T cells induced both autologous and allogeneic B cells to proliferate and to differentiate into Ig secreting cells. Spontaneous culture supernates of T cells obtained from each patient induced substantial proliferation of B cells (B cell-activating activity) as well as proliferation in a standard costimulatory assay (B cell growth factor activity). The culture supernate of a T cell line, which was established from one patient, showed both activities. The T cell line supernate also induced Ig production by staphylococcal A Cowan-activated B cells. None of these properties of AILD T cells was found among 10 normal controls. The addition of AILD T cells to autologous or allogeneic B cells in the presence of pokeweed mitogen (PWM) led to marked suppression of both proliferation and Ig production. This was true even in the presence of fresh normal T cells. Pretreatment studies showed that suppressor cells were induced by the interaction of AILD T cells with PWM-activated B cells. The present study suggests that the B cell hyperactivity observed in AILD patients might in part be due to excessive T cell effects on B cells. In addition, our results may help clarify the paradoxical impaired responsiveness to in vitro stimulation with PWM by active B cells from patients with autoimmune diseases.