Inhibitor (IK) of IFN-γ induced HLA class II antigens expression also inhibits HLA class II constitutive expression in the human Raji B cell line

Abstract

The expression of major histocompatibility complex (MHC) class II antigens is constitutive in professional antigen presenting cells (APCs) but can also be induced by interferon-gamma (IFN-g) on the majority of the non professional APCs (e.g. ®broblasts). We have recently characterised a new factor called IK which is an e cient inhibitor of IFN-g induction of MHC class II antigens expression. Here, we demonstrate a novel role for IK in MHC class II expression since over-expression of this protein by stable transfection into human B cells led to a total disappearance of constitutive MHC class II mRNA expression. The class II transactivator (CIITA) is necessary for both constitutive and IFN-g induced MHC class II expressions. Examination of CIITA mRNA in IK stably transfected clones revealed a marked reduction of CIITA mRNA transcription. Taken together these results demonstrate that the IK protein plays a key role in the constitutive expression of MHC class II antigens and that inhibition induced by IK is upstream of CIITA in this regulatory pathway.

Functional identification of kinases essential for T-cell activation through a genetic suppression screen

“…We utilized a physiologically relevant SAG mediated activation disease model for the T-cell kinase screen in contrast to commonly used stimuli such as PMA or CD3/CD28 induced activation methods. We adapted a previously described method that employs the SAG Staphyloccocus enterotoxin E (SEE) presented by the Raji B cell line that constitutively expresses MHC II proteins to induce activation of Jurkat cells [21,22]. SAGs have diverse structures that share a common mechanism of activity through binding to either the alpha-1 or the beta-1 domains of MHC II expressed on antigen presenting cells.…”

“…2A, B, D), this is not a physiological relevant stimulus for inducing T-cell activation. We, therefore, adopted a method of antigen mediated T-cell activation by the co-culture of Jurkat cells with the antigen presenting Raji B-cell line pretreated with the superantigen Staphyloccocus enterotoxin E [21,22]. The Raji B cells present MHC II bound SEE to the T-cell receptor on the Jurkat cells, initiating a T-cell activation response (Fig.…”

“…Raji cells were pelleted, resuspended to 1.6 × 10 6 cells/ml, SEE added at 1.3 g/ml, followed by 1 h of incubation at 37 • C, 5% CO 2 [21,22]. Jurkat cells were pelleted, resuspended in complete RPMI at 1.6 × 10 6 cells/ml, and added to the Raji cell culture at a ratio of 1:3 Jurkat cells to Raji cells.…”

IK Induced by Coxsackievirus B3 Infection Transiently Downregulates Expression of MHC Class II Through Increasing cAMP

“…It has been reported that IK is an efficient inhibitor of IFNc-induced MHC class II expression and it was originally isolated from the conditioned culture medium of the K562 erythroleukemic cell line (25). IK has also been implicated in the inhibition of constitutive MHC class II expression through the repression of class II transactivator (CIITA) (33,49), a factor that regulates MHC class II expression (10,43). However, the detailed cellular mechanism of IK action remains to be clarified.…”

“…One study showed that the truncated IK (tIK) protein, which includes the 242 amino acids from residue 316 (methionine) to residue 557 (tyrosine), is incapable of localizing in the nucleolus because the 315 amino acid residues are deleted from the N-terminus of the full-length IK protein, but still functions in reducing MHC class II expression (2,33). Therefore, it has been suggested that tIK affects MHC class II expression through its interaction with several unknown cellular factors in the cytoplasm (49). However, the cellular factors that act as adaptors are still unknown.…”