Numerous studies have implicated trans-acting factors in the regulation of MHC class II gene expression. Some of these factors have been shown to act by inducing the expression of class II genes while others have been demonstrated to downregulate such expression. These reports have dealt almost exclusively with the role of trans-acting factors in the regulation of class II gene expression in hematopoietic-derived cells. We decided to extend these studies to the role trans-acting factors play in nonhematopoietic-derived (NHD) cells. In order to address this question we made somatic cell hybrids between the NHD Ltk- cell line and normal B cells to determine if the existence of positive trans-acting factors from the B cell would lead to the expression of Ltk- class II genes in the resultant hybrid. Our results clearly indicate that not only was there no induction of Ltk- class II gene expression in the hybrids, but there was a loss of B cell class II gene expression as well. These results suggest that Ltk- cells possess negative trans-acting factors that appear to predominate over the positive trans-acting factors possessed by B cells. We have further extended these studies to test the MHC-inducing activity of IFN-γ and IL-4 on these hybrids. Our results indicate that the hybrids responded to IFN-γ with an increase in class I but not class II expression for both fusion partners. Furthermore, neither B cell nor L cell class II genes were induced by IL-4. Taken together, these results indicate that Ltk- cells possess negative trans-acting factors that not only maintain the Ia- phenotype of these cells, but also block the action of positive trans-acting factors from B cells.
|Number of pages||14|
|State||Published - Sep 1989|
Bibliographical noteFunding Information:
’ This work was supported by National Institutes of Health Grant CA39070. * Recipient of a National Institutes of Health Postdoctoral Fellowship A107344. [To whom all correspondence should be addressed.] 3 Abbreviations used: NHD, nonhematopoietic-derived, IFN-7, y interferon; IL-4, interleukin 4; MHC, major histocompatibility complex; PEG, polyethylene glycol; FITC, fluorescein isothiocyanate; mAb, monoclonal antibody; FCS, fetal calf serum; Ig, immunoglobulin; FACS, fluorescent-activated cell sorting.
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