Cell-Mediated Inhibition of Proliferation and Activation of Alloreactive Cytotoxic Lymphocytes: Maintenance of Response Potential of Precursors and Dissociation Between Proliferation and Effector Function of Activated Cytotoxic Lymphocytes

Adherent layers of macrophages (Mφ-c) generated in vitro from splenic precursors inhibit lymphoproliferative responses to mitogen and to alloantigen without inhibiting the production of interleukin-2 (IL-2). Analysis of spleen cells stimulated for 48 hr in the presence of Mφ-c indicated that both blastogenesis (increased cell mass) and expression of IL-2 receptors (7D4 determinants) were reduced. Analysis of BrdU incorporation (frequency of S-phase cells) and total cellular DNA revealed that the Mφ-c inhibited the progression from G1 to S phase of cell cycle. The Mφ-c not only inhibited the proliferative response to alloantigen but also prevented the generation of alloreactive cytotoxic T cells. The Mφ-c were shown not to inhibit CTL responses by eliminating the stimulators or by inactivating precursors or inducing suppressors. The Mφ-c were affecting the induction of CTL activity since the Mφ-c did not affect the expression of cytolytic activity by activated CTL. The Mφ-c did inhibit the proliferation of the activated CTL, suggesting that although cytolytic activity can be expressed in G1 phase of cell cycle, the activation of cytolytic activity in CTL-P may require a G1 to S phase transition. The cells recovered from 5-day MLC incubated in the presence of Mφ-c were fully capable of generating a subsequent CTL response. This is in contrast to cells recovered from unstimulated cultures (no Mφ-c) which have lost the ability to generate CTL responses. The Mφ-c therefore prevent the generation of CTL responses in a totally reversible fashion, so as to allow activation and proliferation of CTL-P which have been removed from the influence of the Mφ-c. These observations are discussed in the context of the currently hypothesized role of tissue macrophages in microenvironmental regulation