SIGNAL TRANSDUCTION THROUGH CYTOKINES AND THEIR RECEPTOR FOR B CELL GROWTH AND DIFFERENTIATION

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(1) IL-5, formerly called n-cell-replacing factor (TRF) or B-cell growth factor II, induces Ig- production of activated B cells. Active forms of IL-5 translated in Xenopus oocytes has Mr of 45 to 50 Kd, and migrate to a Mr of 25 to 30 Kd under reducing condition, indicating that mature IL-5 consists of homodimers. Dimer formation is obligatory for the expression of IL-5 activity. Treatment of the IL-5 with N-glycanase in the presence of 2-ME decreased Mr of monomer IL-5 from 25 to 30 Kd to 12 to 14 Kd, indicating that IL-5 is a heavily N-glycosylated protein. Co-injection of tunicamycin and IL-5 MRNA into oocytes induced the production of 27 Kd dimer molecules which exert TRF and BCGF II activity, suggesting that the N-linked carbohydrate moiety does not play an essential role in the biological activity of IL-5.(2) Induction of IgA production by IL-5: Supernatants from PPD-stimulated Tbc-primed T cells can enhance DNP-specific IgA production in cultures of DNP-OVA-stimulated DNP-primed … More B cells.Purified rIL-5 could also enhance anti-DNP IgA production in a dose dependent manner. This enhancing effect was not substituted by IL-1, IL-2, IL-3, or IL-4. Polyclonal IgA secretion of LPS-stimulated B cells was preferentially augmented by IL-5. Surface IgA-positive (sIgA^+) B cells, but not sIgA^- B cells responded to IL-5 for the development of IgA-secreting cells.These results indicate that IL-5 plays an essential role in the antigen-specific and polyclonal IgA-formation. Effects of transforming growth factor-beta (TGF-beta) on IgA production by LPS- stimulated B cells was also studied. TGF-beta itself could selectively augment polyclonal IgA production. TGF-beta) and IL-5 synergistically augmented IgA production. Kinetic analysis for IgA production revealed that TGF-beta exerted its activity early in the culture and IL-5 was required for late in the culture. sIgA^- B cells responded to TGF-beta for the development of IgA-secreting cells. Taking all results together, TGF-beta has differential role in the induction of IgA- production from IL-5 and may induce IgA-specific class-switching and maturation of sIgA^- cells.(3) IL-5 receptor and function: IL-5 acts on target cells via a specific receptor and there are two classes (high- and low-affinity) of IL-5. Cross-linking studies of radiolabeled IL-5 yielded two cross-linked complexes with 92.5 and 160 Kd. Two mabs (H7 and T21) to IL-5 responsive T88-M cells were obtained by immunizing a rat with enriched T88-M cell membranes. MAbs were selected for competitive inhibition of receptor binding of ^<35>S-labeled IL-5 and of IL-5 biological activities. More than 90% of sIgM^<> B cells from peritoneum are H7-positive and 67% of them are also Ly-l^+, and respond to IL-5 for polyclonal IgM production in a high frequency. Finally, both H7 and T21 antibodies specifically precipitate from ^<125>I-labeled IL-5R-positive cell lysates the 60 Kd protein. Less