Characterisation of a novel transmembrane protein in primary human CD4+ T-cells

Abstract

There are two main mechanisms of tolerance, one in the thymus and one in the periphery. Anergy, a peripheral mechanism, is a state of hypo-responsiveness where T-cells fail to respond to antigenic stimulus. A breakdown in immunological self-tolerance leads to autoimmunity and so provides an exciting research area for therapeutic intervention in autoimmune disease. Differential display studies comparing anergic and activated CD4+ T-cells identified claudin domain containing protein 1 (CLDND1) to be differentially expressed between these two states. In addition, preliminary experiments performed in our lab identified CLDND1 as a potential negative regulator of CD4+ T-cell activation. The aim of this study was to identify the role of CLDND1 in CD4+ T-cells. Antibodies against CLDND1 were raised and validated before use to determine CLDND1 expression in immune cell subsets and during T-cell activation. The function of CLDND1 in T-cells was investigated using gene silencing or over-expression techniques. CLDND1 expression was also sought in the autoimmune disease, rheumatoid arthritis (RA), to identify whether CLDND1 may be involved in disease pathogenesis. Antibodies were successfully raised against CLDND1 and CLDND1 was found to be transiently up-regulated during CD4+ T-cell activation. CLDND1 gene silencing attempts, while successful at the RNA level, did not translate to a reduction in CLDND1 protein, suggesting CLDND1 may be regulated independently of gene transcription. Over-expression studies were consistent with CLDND1 being a negative regulator of T-cell proliferation or an inducer of cell death, depending on the activating stimulus used. CLDND1 expression was found to correlate with rheumatoid factor (RF) status in early RA patients and may suggest a role for CLDND1 in the disease setting. Some findings identify similarities between CLDND1 and other proteins, providing links for functional pathways and a plethora of further avenues of research.