NK-dependent increases in CCL22 secretion selectively recruits regulatory T cells to the tumor microenvironment.
Tumor-induced immune suppression involves the accumulation of immune-suppressive infiltrates in the microenvironment. This study demonstrates increased numbers of CD4(+)CD25(+)FoxP3(+) regulatory T cells (Tregs) in the lungs of C57BL/6 mice bearing a metastatic Lewis lung carcinoma (LLC) variant. These Tregs suppressed the proliferation of endogenous CD4(+)CD25(-) cells and expressed higher levels of the chemokine receptor CCR4 than other types of T cells. LLC-bearing lungs secreted elevated levels of the CCR4-associated chemokine CCL22 compared with normal lungs. However, CCL22 was not secreted by LLC or normal epithelial controls, suggesting that CCL22 is secreted by a nonepithelial component of the microenvironment. Migration assays revealed that medium conditioned by LLC-bearing lungs selectively recruited Tregs at higher frequencies than did medium conditioned by normal lungs. Neutralization of CCL22 significantly reduced this selective recruitment toward both conditioned media. A series of immunomagnetic isolations, FACS, and flow cytometric analyses were used to isolate different cellular fractions from both normal and LLC-bearing lungs. When isolated, only the NK-containing fractions secreted CCL22, and the same fraction isolated from LLC-bearing lungs secreted higher levels. Depletion of NK cells from both normal and LLC-bearing lung tissue significantly reduced CCL22 secretion, suggesting that a large portion of secreted CCL22 is NK cell dependent. Flow cytometric analysis of the lung NK compartments revealed no significant increase in NK cell numbers across LLC-bearing lung tissue as a whole as compared with normal tissue. However, immunofluorescent staining revealed an increased frequency of NK cells at the tumor periphery that were closely associated with the elevated FoxP3(+) infiltrate.
Mailloux
Adam W
AW
Department of Microbiology and Immunology, Medical University of South Carolina, Charleston, SC 29403, USA.
Young
M Rita I
MR
D000818:Animals; D018827:Carcinoma, Lewis Lung / Q000276:immunology* / Q000378:metabolism* / Q000556:secondary; D002294:Carcinoma, Squamous Cell / Q000276:immunology / Q000378:metabolism / Q000556:secondary; D002460:Cell Line; D045744:Cell Line, Tumor; D054422:Chemokine CCL22 / Q000096:biosynthesis / Q000378:metabolism*; D002634:Chemotaxis, Leukocyte / Q000276:immunology*; D005260:Female; D007694:Killer Cells, Natural / Q000276:immunology* / Q000378:metabolism* / Q000473:pathology; D008168:Lung / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D008213:Lymphocyte Activation / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D050378:T-Lymphocytes, Regulatory / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D015854:Up-Regulation / Q000276:immunology*
C515483:Ccl22 protein, mouse; D054422:Chemokine CCL22