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Because human lymphotoxin (LT) was originally isolated from a lymphoblastoid cell line, we investigated the role of this molecule in three newly established Epstein-Barr virus (EBV)-infected human B cell lines. These lines were derived from acute lymphoblastic leukemia (Z-6), myelodysplastic syndrome (Z-43), and acute myelogenous leukemia (Z-55) patients who had a prior EBV infection. Each lymphoblastoid cell line had a karyotype that was different from that of the original parent leukemic cells, and all expressed B cell, but not T cell or myeloid surface markers. In all three lines, rearranged immunoglobulin heavy chain joining region (JH) bands were found, and the presence of EBV DNA was confirmed by Southern blotting. Z-6, Z-43, and Z-55 cell lines constitutively produced 192, 48, and 78 U/ml LT, respectively, as assessed by a cytotoxicity assay and antibody neutralization. Levels of tumor necrosis factor (TNF) were undetectable. Scatchard analysis revealed that all the cell lines expressed high-affinity TNF/LT receptors with receptor densities of 4197, 1258, and 1209 sites/cell on Z-6, Z-43, and Z-55, respectively. Furthermore, labeled TNF binding could be reversed by both unlabeled TNF, as well as by LT. Studies with p60 and p80 receptor-specific antibodies revealed that the three lines expressed primarily the p80 form of the TNF receptor. When studied in a clonogenic assay, exogenous LT stimulated proliferation of all three cell lines in a dose-dependent fashion at concentrations ranging from 25 to 500 U/ml. Similar results were obtained with [3H]TdR incorporation. Monoclonal anti-LT neutralizing antibodies at concentrations of 25-500 U/ml inhibited cellular multiplication in a dose-dependent manner. It is interesting that in spite of a common receptor, TNF (1,000 U/ml) had no direct effect on Z-55 cell growth, whereas it partially reversed the stimulatory effect of exogenous LT. In addition, TNF inhibited Z-6 and Z-43 cell proliferation, and its suppressive effect was reversed by exogenous LT. Both p80 and p60 forms of soluble TNF receptors suppressed the lymphoblastoid cell line proliferation and their inhibitory effect was partially reversed by LT. Our data suggest that (a) LT is an autocrine growth factor for EBV-transformed lymphoblastoid B cell lines; and (b) anti-LT antibodies, soluble TNF/LT receptors, and TNF itself can suppress the growth of lymphoblastoid cells, probably by modulating or competing with LT.(ABSTRACT TRUNCATED AT 400 WORDS)

The 16-kD protein constituent of the Mycobacterium tuberculosis complex has been known mainly for its prominent serological immunogenicity and species specificity in tuberculous infection. In this study. we evaluated the T cell immune repertoire in 27 sensitized healthy subjects and 46 patients with active tuberculosis using 14 overlapping 20mer peptides spanning the entire sequence of this protein. Four of the tested peptides individually stimulated proliferation of blood mono- nuclear cells from more than 50% of healthy controls. Tuberculosis patients reacted to a narrower peptide range and with a 17-27% lower rate of responses to the four most immunogenic peptides, but these differences do not distinguish in any simple way between the T cell repertoire of patients and sensitized healthy subjects. The most immunogenic peptide (91-110) was recognized by 67% of healthy subjects and by 50% of tuberculosis patients. Importantly, several non-responders to this peptide were stimulated with the other three most permissive peptides with sequences of 111-130, 71-91 and 21-40, resulting in an overall response rate to at least one of these four peptides of 93% in healthy controls and 74% in tuberculosis patients. ln view of this additive effect between the most immunogenic peptides, their combined use may achieve sufficient sensitivity in a test aimed at the specific discrimination between infected and non-infected healthy subjects. The major interest in testing with these peptides rests in their species specificity. which is not achieved using purified protein derivative (PPD). [ABSTRACT FROM AUTHOR]