The tumour associated cell surface antigen A6H is costimulatory for human CD4+ but not CD8+ T cells

Signalling profiles of circulating leucocytes in patients recovered from reactive arthritis

OBJECTIVES

Reactive arthritis (ReA) is a sterile joint inflammation triggered by a remote infection and associated with human leucocyte antigen (HLA)-B27. Its pathogenesis is unknown, but abnormal response to microbial structures or endogenous inflammatory mediators may be involved. We studied responses in leucocyte signalling profiles in patients with previous ReA after a full recovery.

METHOD

The study comprised 10 HLA-B27-positive healthy subjects with a history of Yersinia enterocolitica-triggered ReA (B27+ReA+) and 20 healthy reference subjects, of whom 10 carried HLA-B27 (B27+ReA-) and 10 did not (B27-ReA-). Phosphospecific fluorescent monoclonal antibodies and flow cytometry were used to determine activation of nuclear factor kappa B (NF-κB), signal transducers and activators of transcription (STATs) 1, 3, 5, and 6, and two mitogen-activated protein (MAP) kinases, p38 and extracellular signal-regulated kinase (ERK)1/2, in monocytes, lymphocytes, lymphocyte subsets, and neutrophils. B27+ReA+ and B27-ReA- whole-blood samples were incubated with Yersinia with or without infliximab to study the role of tumour necrosis factor (TNF) in lymphocyte subset activation. Samples of the three subject groups were studied using soluble bacterial or endogenous stimuli. Fluorescence levels were determined as relative fluorescence units (RFU) and the proportion of positively fluorescing cells.

RESULTS

The intracellular activation of circulating leucocytes in response to soluble stimuli was consistently comparable in B27+ReA+, B27+ReA-, and B27-ReA- subjects. Infliximab inhibited Yersinia-induced lymphocyte NF-κB phosphorylation similarly in B27+ReA+ and B27-ReA- groups.

CONCLUSIONS

ReA susceptibility is not reflected in leucocyte signalling profiles elicited by phlogistic stimuli. However, the possibility remains that aberrations occur in response to combinations of stimuli, such as those associated with leucocyte adhesion.

Identification of the target of monoclonal antibody A6H as dipeptidyl peptidase IV/CD26 by LC MS\MS

The monoclonal antibody (MAb) A6H, originally developed to fetal renal tissues, was found to be highly reactive to renal cell carcinoma and was subsequently demonstrated to co-stimulate a subpopulation of T cells. The A6H antigen had not been identified heretofore. Antigen from detergent extracts of renal cell carcinoma cells (7860) was immunoabsorbed with A6H-agarose, and the resin-bound proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The antigen had a molecular weight of approximately 120 kDa as determined by Western blots. The 120-kDa protein band was excised and subjected to in-gel tryptic digestion, and the resulting peptides were separated and analyzed by liquid chromatography tandem mass spectrometry (LC MS\MS). The tandem mass spectra of the eluting peptides were used in combination with the SEQUEST computer program to search a human National Cancer Institute (NCI) protein database for the identity of the protein. The target antigen was shown to be dipeptidyl peptidase IV (DPP IV), which is also known as the cluster differentiation antigen CD26. Flow analysis of the expression of the A6H antigen and of CD26 on 7860 cells and on peripheral blood lymphocytes supported the identification of the A6H antigen as DPP IV. Recognition that the A6H antigen is DPP IV/CD26 afforded the opportunity to compare previous studies on A6H with those on other anti-CD26 antibodies in terms of expression in cancer cell lines and various tissues and as co-stimulators of T-cell activation.

Selective induction of p38 mitogen-activated protein kinase activity following A6H co-stimulation in primary human CD4(+) T cells

We have recently described the novel A6H antigen expressed on human peripheral blood T cells and on renal cell carcinoma cells. Cross-linking of the A6H antigen results in co-stimulation of human CD4(+) T cells, characterized by induction of the transcription factor activator protein-1 (AP-1), proliferation and prominent IFN-gamma production, but low levels of IL-2. The proximal signaling events associated with A6H ligation include protein tyrosine kinase phosphorylation and association of p56 Lck, ZAP-70 and the TCR zeta chain. In this study we show that A6H co-stimulation selectively induced activation of the p38 mitogen-activated protein kinase (MAPK) pathway, whereas no significant c-Jun N-terminal kinases (JNK) activity was observed. In contrast, CD28 co-stimulation resulted in both p38 and JNK MAPK activities. Human CD4(+) T cells co-stimulated with A6H up-regulated AP-1 binding proteins reactive with a proximal AP-1 binding site in the human IFN-gamma promoter and a consensus AP-1 binding site. Moreover, preincubation of the T cells with the specific p38 MAPK inhibitor SB203580 resulted in decreased AP-1 binding following A6H or CD28 co-stimulation. This suggests that the p38 MAPK pathway is required for induction of full AP-1 binding activity in human CD4(+) T cells co-stimulated with A6H or CD28. Blocking the p38 MAPK pathway by SB203580 completely inhibited IFN-gamma production from A6H co-stimulated T cells and radically reduced IFN-gamma production from T cells co-stimulated with anti-CD28. In contrast, no significant inhibition of IL-2 production was seen after blocking of the p38 MAPK in either A6H or CD28 co-stimulated T cells. Since the p38 MAPK recently has been shown to be critically involved in regulation of IFN-gamma production from T(h)1 cells, we propose that A6H co-stimulation induces a specific pathway, mediated via p38 and AP-1 activation, for induction of a T(h)1 profile in human CD4(+) T cells.