Reversal of T-cell unresponsiveness by T-cell-conditioned medium in retrovirus MAV-2-O-induced immunosuppression in chickens.

Polyclonal activation of T-cells with concanavalin A has been used as an in vitro test system to study immunosuppression induced by the avian retrovirus MAV-2-O. The mitogenic responsiveness of peripheral blood lymphocytes from infected chickens was only weakly suppressed, that of spleen lymphocytes was highly suppressed. Addition of conditioned media rich in T-cell growth factor (TCGF) activity to cultures of infected birds resulted in a reconstitution of the suppressed mitogenic responsiveness up to the level found in lymphocyte cultures from normal chickens. This indicates that the defect of the observed immunopathology is not at the level of responding T-cells. Measurements of TCGF production always showed reduced TCGF levels in the suppressed cultures suggesting that there is a defect at the TCGF production level. This is further supported by the failure to reconstitute the suppressed mitogenic response with normal macrophages, which are involved in activation of TCGF producer T-cells.