IL‐10 indirectly modulates functional activity of CD4⁺CD28null T‐lymphocytes through LFA‐3 and HLA class II inhibition

Expansion of CD4 + CD28 null T‐lymphocytes is common in chronic heart failure (CHF) patients. Its ability to produce high levels of proinflammatory cytokines is probably the key role of these cells in CHF. IL‐10 is a candidate for limiting CD4 + CD28 null T‐lymphocyte responses, whereas tumour necrosis factor (TNF) is the cytokine most closely involved in the loss of CD28 expression. Serum levels of TNF and IL‐10 were measured in 65 CHF patients (mean age, 65.2 ± 13.84 years). Patients with an IL‐10/TNF ratio ≥1 had significantly lower levels of CD4 + CD28 null T‐lymphocytes than those with a ratio <1. In vitro, IL‐10 reduced the frequency of proliferative CD4 + CD28 null T‐lymphocytes stimulated with anti‐CD3. Pre‐treatment with IL‐10 before anti‐CD3 stimulation was required for the cytokine to inhibit TNF production by CD4 + CD28 null T‐lymphocytes. In addition to the previously described effect of IL‐10 on HLA‐DR and ICAM‐1 expression, LFA‐3 protein and mRNA levels were reduced in the presence of the cytokine in monocytes. IL‐10 inhibition on CD4 + CD28 null T‐lymphocytes may be mediated by a reduction in HLA class II and LFA‐3 expression because blocking interactions with these costimulators has similar effects to those of IL‐10 treatment. Moreover, costimulation through CD2/LFA‐3 interaction is enough to induce proliferation and cytokine production in CD4 + CD28 null T‐lymphocytes.