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Spontaneous breakdown of immunological tolerance to gross‐virus‐induced cell‐surface antigens in the rat

WKA/Mk rats injected with undiluted Gross virus at birth demonstrated loss of resistance to transplanted Gross lymphoma (WGT‐4), and also during later life did not contain detectable cytotoxic antibody to Gross virus‐specific cell‐surface antigen. These rats were considered to be immunologically tolerant to the Gross‐virus‐induced cell‐surface antigens, and all of them developed primary Gross lymphoma about 3 months after birth. Some rats injected with diluted virus at birth or undiluted virus at the age of 1 or 2 weeks also continued to be immunologically tolerant to Gross‐virus‐induced cell‐surface antigens for a certain period in proportion to the amount of virus administered, or age at the time of exposure to the virus. Thereafter, this tolerant state was spontaneously broken down and the rats developed transplantation resistance to WGT‐4, and produced cytotoxic antibody to Gross antigens for a considerable period. These rats did not develop Gross lymphoma. These facts suggest that susceptibility to leukemogenesis by the Gross virus in WKA/Mk rats might be ascribed to the immunologically tolerant state to the Gross‐virus‐induced cell‐surface antigens.