The ‘single-stage’ mixed antiglobulin reaction (MAR) was carried out with rabbit thymocytes. This test involved treating the cells with either sheep or goat anti-rabbit globulin sera, and subsequently reacting them with indicator erythrocytes coated with rabbit immunoglobulin (Ig) so as to form rosettes. An unexpectedly high number (up to 38) of thymocytes reacted, although the rosettes were weaker than those given by peripheral B lymphocytes. When blood and lymph node lymphocytes or thymus cells which had already been treated with sheep anti-rabbit globulin serum were subsequently exposed to rabbit anti-sheep Ig serum and then rosetted with indicator cells coated with ox Ig (cross-reacts with sheep Ig) almost 100 reaction was obtained in each of the cell suspensions. This was designated the ‘two-stage’ MAR. The anomalous results, both in the one-stage and two-stage MAR, were abolished by pepsin-treating the sheep anti-rabbit globulin serum; thus indicating that sheep Ig is adsorbed non-specifically via the Fc part of the molecules to the surface of rabbit thymocytes and peripheral T lymp
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