Purpose: Mucins have been implicated in tumor-associated immunosuppression. The possibility that colon cancer mucin (CCM) may modulate T-helper 1 (TH1) activity was evaluated by investigating its effect on the production of interleukin-2 (IL-2) by CD4+ cells, a process that requires antigen-specific and costimulatory signals.
Methods: CCM was purified from human colorectal cancer cells by gel-exclusion fast-pressure liquid chromatography. Cytokine production of purified CD4+ cells was evaluated at the protein and gene level in the presence of a phorbol ester or an anti-CD3 monoclonal antibody (mAb) plus mAb against the CD28 costimulatory receptor to mimic two-signal activation.
Results: Soluble CCM, which contains mucins MUC2 as well as MUC1, inhibited IL-2 mRNA expression and secretion of CD4+ stimulated with a phorbol ester or an anti-CD3 mAb plus anti-CD28 mAb. Pretreatment of CD4+ cells with anti-CD28 mAb abrogated the suppressive effects of CCM on IL-2 production, and flow cytometry showed decreased binding of anti-CD28 mAb to its receptor in the presence of mucin. In addition, Ca2+ mobilization after T cell receptor cross-linking with anti-CD3 mAb was maintained in the presence of CCM. Although interferon gamma production was also diminished, CCM did not induce a general inhibition of cytokine production, nor did it decrease cell viability. Macrophage inflammatory protein 1alpha production was up-regulated; the production of IL-10 and transforming growth factor beta was unchanged.
Conclusions: The results indicate that CCM can alter TH1 activity and suggest that the modulation of costimulatory interactions is involved. They provide another mechanism of immunosuppression mediated by these highly expressed tumor products.