Interaction between human lung fibroblasts and T-lymphocytes prevents activation of CD4+ cells

T lymphocytes are demonstrated to play an important role in several chronic pulmonary inflammatory diseases. In this study we provide evidence that human lung fibroblasts are capable of mutually interacting with T-lymphocytes leading to functionally significant responses by T-cells and fibroblasts.

Human lung fibroblast were co-cultured with PMA-ionomycin activated T-CD4 lymphocytes for 36 hours. Surface as well as intracellular proteins expression, relevant to fibroblasts and lymphocytes activation, were evaluated by means of flow cytometry and RT-PCR. Proliferative responses of T lymphocytes to concanavalin A were evaluated by the MTT assay.

In lung fibroblasts, activated lymphocytes promote an increase of expression of cyclooxygenase-2 and ICAM-1, expressed as mean fluorescence intensity (MFI), from 5.4 +/- 0.9 and 0.7 +/- 0.15 to 9.1 +/- 1.5 and 38.6 +/- 7.8, respectively. Fibroblasts, in turn, induce a significant reduction of transcription and protein expression of CD69, LFA-1 and CD28 in activated lymphocytes and CD3 in resting lymphocytes. In activated T lymphocytes, LFA-1, CD28 and CD69 expression was 16.6 +/- 0.7, 18.9 +/- 1.9 and 6.6 +/- 1.3, respectively, and was significantly reduced by fibroblasts to 9.4 +/- 0.7, 9.4 +/- 1.4 and 3.5 +/- 1.0. CD3 expression in resting lymphocytes was 11.9 +/- 1.4 and was significantly reduced by fibroblasts to 6.4 +/- 1.1. Intracellular cytokines, TNF-alpha and IL-10, were evaluated in T lymphocytes. Co-incubation with fibroblasts reduced the number of TNF-alpha positive lymphocytes from 54.4% +/- 6.12 to 30.8 +/- 2.8, while IL-10 positive cells were unaffected. Finally, co-culture with fibroblasts significantly reduced Con A proliferative response of T lymphocytes, measured as MTT absorbance, from 0.24 +/- 0.02 nm to 0.16 +/- 0.02 nm. Interestingly, while the activation of fibroblasts is mediated by a soluble factor, a cognate interaction ICAM-1 mediated was demonstrated to be responsible for the modulation of LFA-1, CD28 and CD69.

Findings from this study suggest that fibroblasts play a role in the local regulation of the immune response, being able to modulate effector functions of cells recruited into sites of inflammation.