THE DIFFERENTIAL EFFECT OF ALLOANTIGEN-BLOCKING ANTIBODIES ON UNPRIMED AND MEMORY T-HELPER CELLS

Responsiveness to recall antigens by memory and naive T helper cells i s different. To study whether such a difference is also applicable to affinity for allorecognition, we analyzed the effect of an IgG MLR blo cking antibody separated from sera of patients with known kidney trans plant chronic rejection on primed and unprimed CD4(+) T cell alloreact ivity. The results show that addition of the IgG fraction inhibits the patient's own unprimed T helper cell responses to a panel of four dif ferent alloantigens as well as a third-party mixed lymphocyte response . The same IgG fraction inhibited third-party naive T helper cell, but not autologous unprimed T helper cell, proliferation to adherent anti -CD3 antibody, which suggests that the mechanism of inhibitory action of the IgG is allogeneic-dependent. This IgG also did not induce inhib ition of any of the T helper cell clone responsiveness, raised from th e same or other patients, when stimulated with the same alloantigens u sed for unprimed cell alloactivation. Differential responses of naive and memory CD4(+) T cells to alloantigens may explain some differences between the in vivo and in vitro systems and why allograft rejection can proceed in the presence of allogeneic blocking antibodies.