The occurrence of chicken foetal antigen after infection with Marek's disease virus in three strains of chicken.

An indirect immunofluorescence procedure employing specific antiserum was used to demonstrate chicken foetal antigen (CFA), a membrane antigen typically present on embryonic cells. The expression of CFA by lymphocytes from the peripheral blood, spleen, thymus and bursa was found to decline rapidly after hatching; the bursa, however, contained about 30% CFA-positive cells until at least 120 days of age. After infection of a genetically susceptible strain of chickens (HPRS Rhode Island Red) with Marek's disease virus, the expression of CFA by lymphocytes in the blood and lymphoid organs was found to increase steadily. Lymphomas which developed contained, on average, 25.7% CFA-expressing cells. In contrast, a second susceptible strain (line 7) showed no increase in CFA expression (compared with uninfected controls), and lymphomas from these birds contained only 4.8% positive cells. A genetically resistant strain (line 6) also did not differ from uninfected controls. It was concluded that in Marek's disease, CFA expression is associated with malignant transformation, although transformation may occur without the appearance of CFA, and that CFA is a marker for a stage of dedifferentiation of transformed cells rather than a marker for transformation. The degree of dedifferentiation seems to vary from strain to strain.