Induction of long-term specific tolerance to allografts in rats by therapy with an anti-CD3-like monoclonal antibody.

Monoclonal antibodies to CD3 have been shown to activate T cells in vivo and in vitro but have also been shown to render T cells anergic in vitro. In this study G4.18, a mouse IgG3 mAb, was produced that appeared to recognize CD3 by its binding to all peripheral T cells, including a population not recognized by mAb to TCR-alpha/beta that was presumed to be TCR-gamma/delta cells. It precipitated molecules in the 24-26 kd region consistent with the CD3 complex as well as molecules approximately 45 and approximately 49 kd that corresponded to TCR alpha and beta chains and a 92-kd complex. Incubating T cells for 24 hr with saturating concentrations of G4.18 caused modulation of the TCR complex. In vitro, it activated T cells but only if prebound to plastic. In solution it inhibited MLC and CML, but not PHA or Con A activation. In vivo, G4.18 was not toxic even in high doses, and this was thought to be due to the inability of this mAb to activate T cells in vitro because the rat lacks Fc receptors for mouse IgG3. Therapy with G4.18 resulted in transient modulation of TCR/CD3 on T cells and depletion of these cells from blood. G4.18 had no depleting effects by lymph node or spleen cells but caused marked, transient thymic involution. Therapy with G4.18 also induced indefinite survival (> 100 days) of PVG (RTIc) heart grafts but not skin grafts in DA (RTIa) hosts. These hosts with long-surviving cardiac transplants, when grafted from PVG skin, accepted these grafts but rejected third-party skin in first-set. Thus G4.18 was shown to induce long-term specific tolerance to an organ allograft.

Induction of isotype switching and Ig production by CD5+ and CD10+ human fetal B cells.

In the present study the capacity of early fetal B cells to produce Ig was investigated. It is shown that B cells from fetal liver, spleen, and bone marrow (BM) can be induced to produce IgM, IgG, IgG4, and IgE, but not IgA, in response to IL-4 in the presence of anti-CD40 mAb or cloned CD4+ T cells. Even splenic B cells from a human fetus of only 12 wk of gestation produced these Ig isotypes. IFN-alpha, IFN-gamma, and transforming growth factor-beta inhibited IL-4-induced IgE production in fetal B cells, as described for mature B cells. The majority of B cells in fetal spleen expressed CD5 and CD10 and greater than 99% of B cells in fetal BM were CD10+. Highly purified CD10+, CD19+ immature B cells and CD5+, CD19+ B cells could be induced to produce Ig, including IgG4 and IgE, in similar amounts as unseparated CD19+ B cells. Virtually all CD19+ cells still expressed CD10 after 12 days of culture. However, the IgE-producing cells at the end of the culture period were found in the CD19-,CD10- cell population, suggesting differentiation of CD19+,CD10+ B cells into CD19-,CD10- plasma cells. Pre-B cells are characterized by their lack of expression of surface IgM (sIgM). Only 30 to 40% of BM B cells expressed sIgM. However, in contrast to sIgM+,CD10+,CD19+ immature B cells, sorted sIgM-,CD10+,CD19+ pre-B cells failed to differentiate into Ig-secreting cells under the present culture conditions. Addition of IL-6 to these cultures was ineffective. Taken together, these results indicate that fetal CD5+ and CD10+ B cells are mature in their capacity to be induced to Ig isotype switching in vitro as soon as they express sIgM.

Membranes of activated CD4+ T cells expressing T cell receptor (TcR) alpha beta or TcR gamma delta induce IgE synthesis by human B cells in the presence of interleukin-4.

In the present study it is demonstrated that human B cells can be induced to switch to IgE production following a contact-mediated signal provided by activated T cell receptor (TcR) gamma delta+, CD4+ and TcR alpha beta+, CD4+ T cell clones and interleukin (IL)-4. The signal provided by these T cell clones was antigen nonspecific, indicating that the TcR alpha beta/CD3 or TcR gamma delta/CD3 complexes were not involved in these T-B cell interactions. Activated TcR alpha beta+, CD8+, and TcR gamma delta+, CD4-CD8-, or resting CD4+ T cell clones were ineffective. Intact TcR alpha beta+ or TcR gamma delta+, CD4+ T cell clones could be replaced by plasma membrane-enriched fractions isolated from these activated CD4+ T cell clones. In contrast, membranes isolated from resting TcR alpha beta+, CD4+, TcR gamma delta+, CD4+ T cell clones or an Epstein-Barr virus (EBV)-transformed B cell line (EBV-LCL) failed to provide the costimulatory signal that, in addition to IL-4, is required for induction of IgE synthesis. As described for intact CD4+ T cells, CD4+ T cell membranes induced purified surface IgM+ B cells to switch to IgG4- and IgE- but not to IgA-producing cells, excluding the possibility of a preferential outgrowth of IgG4- and IgE-committed B cells. The membrane activity was inhibited by protease or heat treatment. Induction of IgE synthesis by B cells co-cultured with both TcR alpha beta+, CD4+ and TcR gamma delta+, CD4+ T cell clones and membrane preparations of these cells was blocked by anti-class II major histocompatibility complex (MHC) monoclonal antibodies (mAb), whereas various anti-CD4 mAb had differential blocking effects. Murine L cells, or EBV-LCL transfected with CD4 could not replace CD4+ T cell clones. These results indicate that, although CD4 and class II MHC antigens are required for productive CD4+ T cell clone-B cell interactions, an additional signal, provided by a membrane associated (glyco)protein that is induced by activation of both TcR alpha beta and TcR gamma delta, CD4+ T cells, is needed for induction of IgE production in the presence of IL-4.

Regulation of IgE synthesis by cytokines.

Considerable progress has been made in our understanding of the mechanisms underlying regulation of human IgE synthesis. Interleukin-4 induces IgE production specifically, but costimulatory signals provided by T cells are required. Other cytokines modulate interleukin-4-induced IgE synthesis. The roles of T cells and cytokines in regulating IgE switching are discussed.

A6--a new 45RO monoclonal antibody for immunostaining of paraffin-embedded tissues.

The authors report on the extensive characterization, on normal and pathologic tissues, of the T-cell-specific monoclonal antibody (MoAb) A6, which the authors previously found to identify a fixation- and paraffin-embedding-resistant epitope. A6 reacted with most T lymphocytes, macrophages, and Langerhans' cells of normal tissues and with peripheral T-cell lymphomas (31 of 34), Ki-1+ lymphomas (12 of 18), and T-cell leukemias (1 of 5). All cases of X and non-X histiocytosis examined and monocytic leukemias with mature phenotype only were A6 positive. Three of 47 cases of B-cell lymphoma and leukemia were labeled. Hairy cell leukemias, multiple myelomas, and Hodgkin's and Reed-Sternberg cells were negative. The A6 reactivity was preserved with different fixatives (formalin, Bouin's fluid, Carnoy's fixative, and B5) and decalcification procedures and was slightly enhanced by trypsin digestion. The pattern of reactivity of A6 was similar to that obtained with MoAb UCHL-1, recognizing the CD45RO determinant of leukocyte common antigen; however, in pathologic tissues, A6 labeled a higher percentage of cells than UCHL-1. Cross-blocking and enzyme digestion studies (Pronase E [Sigma Chemical, St. Louis, MO] and neuraminidase [Sigma Chemical]) indicated that the two MoAbs may identify close epitopes on the same molecule. In conclusion, the authors' study indicates that A6 is an excellent reagent for detection of the CD45RO molecule on paraffin-embedded normal and pathologic tissues.