FIGURE 5.

Inhibitory cells can be differentiated into functionally mature, activating APC under the influence of combined GM-CSF and IL-4. To assess the influences of GM-CSF and IL-4 alone or in combination on the differentiation of inhibitory cells, we isolated Gr-1⁺ splenocytes from mice that had received TS/A tumor inoculation. Inhibitory cells were then exposed to either no cytokines, GM-CSF alone, IL-4 alone, or a combination of GM-CSF and IL-4. After 6 days of culture, these cells were tested for their function (A) and phenotype (B). A, Cytokine-treated inhibitory cells were added at a final concentration of 0.18 × 10⁶ cells (3%) to a MLC consisting of 3 × 10⁶ BALB/c splenocytes (H-2^d) together with an equal number of γ-irradiated C57BL/6n splenocytes (H-2^b). The MLC was assessed in a standard ⁵¹Cr release assay for activity after an additional 6 days of culture using an H-2^b target, MBL-2, and a control H-2^d target, CT26, at E:T ratios starting at 100:1, followed by 3-fold dilutions (100:1, 33:1, 11:1, 4:1, 1:1, 0.4:1). B, Phenotypic characterization of cells after the 6-day cytokine regimen. Isotype matched controls are shaded.