CD19+CD10+ human B lineage bone marrow cells were separated into cycling or resting cells, which differ in their expression of CD34, VpreB, recombination activating gene (RAG-1), and terminal deoxynucleotidyl transferase (TdT). Polymerase chain reaction analyses developed for DHJH and VκJκ, VκJκK(de) and VκK(de) rearrangements with DNA of single cells and a comparison with B lineage cell development in mouse bone marrow, allow to delineate the human B lymphocyte pathway of development as follows: CD34+VpreB +RAG-1+TdT+, DHJH-rearranged, κL germline cycling pre-B I cells → CD34−VpreB +μH chain+ (pre-B receptor+) RAG-1−TdT−, VHDHJH-rearranged, κL germline, cycling pre-B II cells → CD34−VpreB −, intracytoplasmic μH chain+ (pre-B receptor−) RAG-1+/− TdT−, VHDHJH-rearranged, mainly κL germline cycling pre-B II cells → CD34−VpreB − intracytoplasmic μH chain+, RAG-1+TdT−, VHDHJH-rearranged, VκJκ-rearranged, IgM−, resting pre-B II cells CD34+VpreB −, sIgM+, RAG-1+TdT−, VHDHJH- and VκJκ-rearranged IgM+ immature B cells → CD34−, CD10−, sIgM+/sIgD+ mature B cells. This order, for the first time established for human B lineage cells, shows striking similarities with that established for mouse B lineage cells in bone marrow.

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Whether there is one or multiple ␣␤T cell antigen receptor (TCR) recognition modules in a given TCR͞ CD3 complex is a long-standing controversy in immunology. We show that T cells from transgenic mice that coexpress comparable amounts of two distinct TCR␤ chains incorporate at least two ␣␤TCRs in a single TCR͞CD3 complex. Evidence for bispecific ␣␤TCRs was obtained by immunoprecipitation and immunoblotting and confirmed on the surface of living cells both by f luorescence resonance energy transfer and comodulation assays by using antibodies specific for TCR␤-variable regions. Such (␣␤) 2 TCR͞CD3 or higher-order complexes were evident in T cells studied either ex vivo or after expansion in vitro. T cell activation is thought by many, but not all, to require TCR cross-linking by its antigen͞major histocompatibility complex ligand. The implications of a multivalent (␣␤) 2 TCR͞CD3 complex stoichiometry for the ordered docking of specific antigen͞major histocompatibility complex, CD4, or CD8 coreceptors and additional TCRs are discussed.The T cell receptor complex (TCR͞CD3) consists of disulfidelinked ␣␤ heterodimers noncovalently associated with invariant proteins of the CD3 (CD3␥, ␦, and ) and the (, , and FcRI␥) families (1-3). The TCR␣ and TCR␤ components contain variable (V) and constant (C) domains homologous to those of antibodies (Ig), but they are not secreted and recognize antigen fragments embedded in molecules of the major histocompatibility complex (MHC) (4-6). The CD3͞ subunits have both signaling and structural functions (7,8). Whether one or multiple ␣␤TCR heterodimers occur in a TCR͞CD3 complex currently is unresolved. A reassessment of TCR stoichiometry began after the finding that two CD3 chains occur per TCR͞CD3 complex (9, 10), because early studies indicated a 1:1 ratio for TCR͞CD3 chains using mAbs to TCR and CD3 for estimation of the number of binding sites (1). On the one hand, several groups have suggested that TCR, like Ig, is multivalent, [i.e., (␣␤) 2 TCR and (HϩL) 2 Ig]. It was argued that such an arrangement: i) maximizes the interactions between charged transmembrane residues in ␣␤TCR (3 ϩ ) and CD3͞ (6 Ϫ ) chains, rendering a more stable complex, and ii) fits with the hydrodynamic measurements of TCR͞CD3 complex size (11-13). On the other hand, recent biochemical analyses argue against a multivalent TCR model because immunoprecipitations with mAb to V ␣ or V ␤ failed to reveal the predicted association of two TCR␣s or two TCR␤s in lysates of T cells bearing two distinct ␣␤TCRs (14, 15).Previous studies of the TCR͞CD3 subunit stoichiometry (9, 10, 15) have relied on the ability to coprecipitate from surface-labeled cells two homologous forms of a given subunit that were distinguishable after gel electrophoresis and autoradiography. Although such an experimental design allowed to show that two CD3 subunits, of human and mouse origin, occur per TCR͞CD3 complex (9, 10), it may be not of universal application. We and others have noticed that the similarity between two distinct TCR␣...

Selective intracoronary infusion of BDM at doses inhibiting regional wall motion decreased infarct size after reperfusion. The effects of BDM on regional function, the reduction in contraction band necrosis at histology, and the peculiar configuration of these infarcts all suggest that inhibition of contracture can interfere with cell-to-cell progression of myocardial necrosis, supporting a role for contracture in reperfusion-induced cell death.