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Human peripheral blood B lymphocytes can be activated by pokeweed mitogen (PWM) 1, Staphylococcus aureus Cowan I, Epstein-Barr virus, or Nocardia water-soluble mitogen (1-4). Of these polyclonal activators, PWM and S. aureus have been shown to stimulate both B and T cells; furthermore, the activation of peripheral blood B cells by PWM appears to be T cell dependent (5, 6). Nocardia mitogen, Epstein-Barr virus, and S. aureus Cowan I have been shown to be relatively T cell-independent B cell activators (2-4).Several parameters can be used to evaluate the polyclonal "activation" of human peripheral blood B lymphocytes, including immunoglobulin (Ig) production in vitro, enumeration of Ig-secreting cells by reverse hemolytic plaque assay, and enumeration of intracytoplasmic Ig-containing cells in stimulated cultures. However, study of human peripheral blood B lymphocyte function in normal and disease states has been hampered by the failure of mature human B cells to respond to some classic activators of murine B cells, such as dextran sulfate, tuberculin (PPD), and Escherichia coli lipopolysaccharide (LPS) (7-10). Dextran sulfate activates relatively immature murine B cells and results predominantly in increased DNA synthesis; in contrast, PPD acts on relatively mature murine B cells and stimulates a marked increase in antibody production but only modest DNA synthesis (11). However, PPD and other polyelonal B cell activators (PBA) that activate mouse B cells do not have the same effects on human peripheral blood B lymphocytes.The ability to stimulate human B cells selectively would be of considerable value for studies of immune function. We describe here a "new" PBA, i.e., formaldehydefixed Salmonella paratyphi B, which activates human peripheral blood B cells to produce large amounts of Ig but does not stimulate DNA synthesis as measured by incorporation of tritiated thymidine. This PBA apparently acts on relatively mature B cells * Publication 381 from the

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SUMMARY The human Thy‐1 homologue (p25) was characterized biochemically for amino acid composition, sequence and carbohydrate content. Two other forms of the human Thy‐1 molecule were detected and partially characterized. A 40,000 mol.wt. molecule (p40) is the dimer of p25 and its formation is increased by the presence of sodium dodecyl sulphate (SDS). The second form of 16,000 mol.wt. (p16) appears to be a cryptic or breakdown form of p25. Comparison of the amino acid compositions of p25, p40 and p16 isolated from MOLT‐3 cells, with that deduced from the nucleotide sequence of the gene coding for part of the putative T cell antigen receptor, also from MOLT‐3 cells, shows that the Thy‐1 homologue is distinct from, but evolutionary related to, one of the putative T cell antigen receptor polypeptide chains.

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