CD4 mAb therapy modulates alloantibody production and intracardiac graft deposition in association with selective inhibition of Th1 lymphokines.

The accelerated (24 h) rejection of (LEWxBN)F1 cardiac allografts (Tx) in LEW rats sensitized with BN skin grafts, is abrogated with CD4 mAb (BWH-4) administration between skin (day -7) and heart (day 0) transplantation (Tx survival ca. 11 days, p < 0.0001). This study analyzed the effects of CD4-targeted therapy upon host IgG and IgM alloantibody (allo-Ab) within the serum by two-color flow cytometry, and within the Tx, by immunohistology. These data were correlated with mRNA and protein production profiles of Th1 (IL-2, IFN-gamma) vs Th2 (IL-4) specific cytokines (polymerase chain reaction and/or immunohistology). Skin grafts elicited a strong systemic IgM allo-Ab response, which peaked at the time of cardiac Tx rejection at 24 h. It was associated with extensive deposits of IgM on Tx endothelium. Treatment with BWH-4 mAb diminished circulating IgM allo-Ab levels, and only low levels of IgM could be detected at the Tx site. Conversely, the low circulating IgG allo-Ab levels during rejection at 24 h in untreated recipients were accompanied by a strong labeling for intra-Tx IgG. BWH-4 mAb therapy did not prevent totally the switch of the IgM to IgG, but the IgG allo-Ab response was earlier, less intense and more transient than in untreated recipients. Accelerated rejection triggered sequential lymphokine mRNA expression in cardiac Tx, with the peak of transcription for IL-2 (6-12 h) preceding that for IL-4 (24 h). Interestingly, although CD4 targeted therapy virtually ablated the induction of IL-2 mRNA, it preserved transcription of the IL-4 gene. BWH-4 mAb therapy decreased otherwise abundant intra-Tx IL-2 and IFN-gamma, but allowed a vigorous elaboration of IL-4, confirming the translation of mRNA to the protein in vivo. Thus, CD4 mAb-mediated abrogation of accelerated cardiac Tx injury correlates with suppression of Th1 responses (depressed IL-2 and IFN-gamma production), but sparing of the Th2 function (enhanced IL-4 elaboration). Indeed, CD4 mAb-induced allo-Ab depression and immunosuppressive effects may reflect selective targeting of proinflammatory Th1-like cells and the multifaceted effects of IL-4 produced by unopposed Th2-like cells.