Expression of complement regulator proteins in primary and metastatic malignant melanoma

The expression of complement regulatory antigens C3b/C4b receptor, (CD35) m embrane cofactor protein (CD46), decay accelerating factor (CD55), and homo logous restriction factor 20 (CD59) was determined immunohistochemically on ten primary malignant melanomas, 16 metastatic lesions, and ten melanocyti c nevi. All of the melanocytic nevi and 9/10 primary melanomas showed both expression of CD46 and CD59. In one primary melanoma lacking CD46, expressi on of CD35 could be detected. In metastatic melanoma, 9/16 metastases were CD46+/CD59+, two were CD46-/CD59+, one CD46+/ CD59-, and four CD46-/CD59-. Additionally, CD55 could be detected in two CD46+/CD59+ metastases, and CD3 5 in one. Expression or lack of complement regulatory antigens did not corr elate with the expression of GD2, GD3, HMB-45 or S-100. fn conclusion, some cases of metastatic melanoma show loss of normal expression of complement regulatory proteins. This might have implications on the immune response or the efficacy of immune therapy in malignant melanoma.