Analysis of the Biological Function of CD5 Molecule.

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In order to define biological function of the CD5 (T1, Leu1, Tp67) molecule, a cDNA clone of CD5 was expressed in a CD5 deficient Jurkat cell line and in a murine T cell hybridoma. A Jurkat subclone (Jurkat 9.9) produced interleukin-2 (IL-2) in response to anti-CD3 monoclonal antibody (MAB) crosslinked to solid support. IL-2 production was enhanced by co-culture with the anti-CD5 MAb OKT1. A CD5 deficient mutant clone Jurkat 1.15 was generated by treatment with ethyl methanesulfonate followed by selection with anti-CD5 MAb plus complement. Jurkat 1.15 did not demonstrate enhancement of IL-2 production by OKT1 in the presence of crosslinked anti-CD3 MAb. A cDNA encoding CD5 was introduced into a defective retrovirus which was used to infect Jurkat 1.15. A Jurkat clone stably expressing CD5 was established. In response to OKT1, a rise in intracellular calcium was observed in both the parent Jurkat 9.9 and the CD5 positive infectant but not in the CD5 negative mutant or a G418 resistant c … More ontrol. Furthermore, expression of CD5 restored the augmentation of Il-2 production by OKT1 in response to crosslinked anti-CD3 MAb. A murine T cell hybridoma By155.16 which produces IL-2 in response to HLA-DR antigens was also infected with the CD5 recombinant retrovirus and three stable CD5 positive infectants were generated. These hybridomas showed enhancement of Il-2 production by stimulation with OKT1 in the presence of suboptimal concetrations of soluble anti-murine CD3 MAb. These results provide further evidence that CD5 provides a costimulatory signal for T cell activation.The role of the CD5 surface molecule in T cell responsiveness to interleukin-1 (IL-1) was examined. The CD5+ wild type Jurkat 9.9 produced interleukin-2 (IL-2) in response to anti-CD3 monoclonal antibocy (MAb), OKT3, crosslinked to a solid surface. IL-2 production was enhanced by co-culture with IL-1 or anti-CD5 MAb. Neither the CD5- mutant nor the CD5- G418-resistant infectant responded to anti-CD5 MAb or to IL-1. Responsiveness to IL-1 was restored by cell surface expression of CD5 in the CD5+ infectant. Both the CD5+ wild type Jurkat and the CD5+ infectant responded equivalent to purified IL-1, recomvinant IL-1alpha and recobinant IL-1beta. Optimal concentrations of IL-1and anti-CD5 MAb had an additive effect upon the enhancement of IL-2 production stimulated with crosslinked anti-CD3 MAb suggesting that IL-1 and CD5 act through distinct pathways. The specific binding of recombinant IL-1beta was examined in these cell lines. Both the specific binding (at 4ﾟC) and subsequent internalization (at 37ﾟC) of 125I labeled recombinant IL-1beta was equivalent in the CD5+ infectant and the CD5+ wild type Jurkat cell, whereas specific binding of ^<125>I labeled recombinant I1-1beta was markedly decreased in the CD5- G418-resistant infectant. These observations strongly suggest that cell surface expression of CD5 regulates binding of and responsiveness to IL-1. Less