CD28 EXPRESSION IS INCREASED IN VENOM ALLERGIC PATIENTS BUT IS NOT MODIFIED BY SPECIFIC IMMUNOTHERAPY

Background Recognition of antigen bound to the major histocompatibilit y complex by the T cell receptor is insufficient to lead to T cell pro liferation and effector function, which require co-stimulatory signals , such as those resulting from the interaction of CD28 expressed on T lymphocytes and CD80/CD86 expressed on APCs. Lack of interaction betwe en these accessory molecules during antigen stimulation leads to a sta te of antigen-specific lymphocyte unresponsiveness. Previous studies h ave shown that rush venom immunotherapy decreases venom-specific T cel l proliferation very early after the initiation of the rush. Objective In order to see whether this hyporeactivity was associated with a dow n regulation of accessory molecules, we studied CD28 surface expressio n on T lymphocytes from 10 non-atopic controls and from 10 non-atopic patients undergoing rush venom immunotherapy. Methods Peripheral blood samples were collected before the rush (day 0), at the end of the rus h (day 1), at day 15 and at day 45. CD28 expression was analysed using flow cytometry with double labelling of the CD4(+) and CD8(+) lymphoc yte subpopulations. Results At baseline CD28 was expressed at a higher level on T lymphocytes from allergic patients than from control subje cts (P < 0.04), and in particular on the CD8 subset (P < 0.01), reflec ting a decrease in the suppressive CD8(+)CD28(-) subpopulation. No cha nges were found in the percentages of total CD28(+) T cells, CD4(+)CD2 8(+) or CD8(+)CD28(+) cells at the different time points after the ini tiation of immunotherapy. Conclusion These results suggest that the CD 28 pathway is probably involved in the development of allergic reactio ns, but at least at the phenotypic level, CD28 expression remained unc hanged after rush venom immunotherapy.