A lack of evidence for down‐modulation of CD3ζ expression in colorectal carcinoma and pregnancy using multiple detection methods

Loss of the T cell receptor‐associated CD3 ζ chain has been proposed as a possible mechanism of the acquired immunosuppression in both tumour‐bearing hosts, and in symptomatic patients with HIV infection. However, other reports suggest that the ζ‐chain loss may in part be caused by protease activity of contaminating phagocytes ex vivo. Using flow cytometry and Western blot analysis on highly purified T cells, and ensuring adequate addition of protease inhibitors, we have studied the expression of CD3ζ on peripheral blood T cells from patients with colorectal carcinoma, and compared these with normal controls, and pregnant donors, as a further example of an immunocompromised state. Immunohistochemistry was performed on tumour sections from patients with colorectal carcinoma to measure CD3ζ expression in tumour infiltrating T cells, and compared with normal mucosa and tonsil. Using these three approaches, our data provide no evidence for downregulation of CD3ζ chain expression either in colorectal carcinoma or pregnancy and suggest that this explanation is unlikely to fully account for the reduced T cell function associated with these conditions in all patients.