Lung mucosal Th2 responses are regulated by CD4+CD25+ suppressor T cells

Abstract

In recent years, a subset of CD4+CD25+ T cells has been described that regulates cell mediated immune responses. Although CD4+CD25+ T cells prevent the development of autoimmunity their role in limiting allergic inflammation and their mode of action is not clearly understood. To investigate the role of regulatory T cells in airway inflammation, we have developed a model using the DO11.10 mouse which expresses a OVA specific T cell receptor.

FACS analysis revealed that 6.8% of CD4+ T lymphocytes in the lymph nodes of DO11.10 mice were CD4+CD25+. CD4+CD25+ T cells were purified by magnetic bead separation to a purity of 70-75 %. These CD4+CD25+ T cells mediated regulatory activity since they were effective at inhibiting T cell responses to anti-CD3. Although DO11.10 CD4+CD25+ T cells were anergic it was found that they could be expanded and polarised in vitro in the presence of OVA_323-339 peptide and exogenous IL-2 and IL-4. Expanded CD4+CD25+ T cells expressed an OVA specific T-cell receptor (97-98% KJ1-26+) and were effective at inhibiting T cell proliferative responses to either OVA_323-339 or anti-CD3.

Total CD4+, CD4+CD25+ and CD4+CD25- T cells were analysed for the differential expression of adhesion molecules. FACS analysis revealed that CD44 was a predominant adhesion molecule expressed by all 3 groups. Total CD4+ and CD4+CD25- expressed β7 chain, CD62L and CD31 but the level of expression was lower than CD44. It was also found that PLN cells expressed CD103, but its expression was lost following the expansion of these cells in culture.

The effect of CD4+CD25+ T cells on Th2 polarization and allergic inflammation in vivo was examined. Th2 cells were either generated from unfractionated CD4+ T cells or CD4+ T cells depleted of CD4+CD25+ cells prior to polarization. Depletion of CD4+CD25+ T cells markedly influenced anti-CD3 stimulated cytokine production by Th2 polarised cells. The level of IL-4, IL-5 and IL-13 produced by Th2 cells generated from CD4+CD25- T cells was markedly lower than that by unfractionated CD4+ T cells. This reduced cytokine production was evident irrespective of the concentration of anti-CD3 used.  Interestingly, cultured CD4+ CD25+ regulatory T cells inhibited IL-4 but not IL-5 production by Th2 cells.

The effect of depleting CD4+CD25+ T cells on airway inflammation was assessed in vivo. A marked pulmonary eosinphilia could be induced following transfer of DO11.10 Th2 cells if recipients were exposed to OVA aerosols. Recipient mice were exposed to aerosolised OVA for 7 consecutive days and then sacrificed on the last day. The number of CD4+KJ1-26+ T cells in the BALF and associated eosinophilia increased from no detectable inflammation until 5 days of aerosol challenge.

Collectively, these studies demonstrate that CD4+CD25+ T cells influence both Th2 polarization and the development of pulmonary inflammation.

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