Understanding the functional role of CCR4 and CCR8 in type-1 and type-2 granulomatous immune responses

Immune granulomas are focal accumulations of macrophages and inflammatory cells observed in numerous disease conditions. Chemokines and their receptors are implicated in driving cellular recruitment during granuloma formation. To elucidate underlying mechanisms, we developed murine models of synchronized T-cell-mediated pulmonary granuloma formation. Sensitization followed by re-challenge with either matrix-bound Mycobacteria bovis purified protein derivative or Schistosoma mansoni egg antigens establishes type-1 or type-2 granulomas, respectively. Using these models, we tested the in vivo function of selected chemokine receptors in granuloma formation. Previous in vitro studies suggested that chemokine receptors demonstrated restricted expression. Th2 cells reportedly expressed CCR3, CCR4, and CCR8. Therefore, we hypothesized that CCR4 and CCR8 would act as functional Th2 effector cell receptors necessary for maximal type-2 granuloma formation; however, our in vivo studies refute this hypothesis.;Studies utilizing CCR4 deficient (CCR4-/-) mice revealed normal type-2 responses but impaired type-1 memory responses, manifest as decreased lesion size and IFNgamma production. The CCR4-/- Th1 cells were impaired, as adoptive transfer of sensitized CCR4-/- CD4+ T-cells were unable to elicit a type-1 response in wild-type mice. Yet attempts to reconstitute CCR4-/- mice with wild-type CD4+ T-cells failed to correct defects, suggesting the necessity of another CCR4+ population. Our studies implicated dendritic cells (DCs) as CCR4+/+ CD4+ T-cells co-cultured with CCR4-/- DCs demonstrated impaired IFNgamma production. Thus, CCR4 was required to establish and elicit maximal Th1 granulomatous responses.;A similar analysis of pulmonary granuloma formation in CCR8-/- mice revealed impaired type-2 responses; however, this was not attributed to defective IL-4-producing Th2 cells. Instead, CCR8 associated with CD4+CD25+IL-10-producing regulatory T-cells. The importance of this population in type-2 granuloma formation was revealed when wild-type CD4+ T-cells lost the ability to correct defects in CCR8-/- mice upon removal of IL-10-producing cells. Thus, fully polarized type-2 responses required permissive regulation by CCR8+IL-10-producing T-cells.;Taken together our studies indicate that chemokine receptor expression in vivo is more complex and dynamic than in vitro polarization studies suggested. We demonstrate different mechanisms of participation for CCR4 and CCR8 in polarized models of type-1 and type-2 lung granuloma formation, offering potential for selective therapeutic interventions utilizing chemokine receptor targeting.