MS4a4B augments IL-2 production from stimulated T cells. (A) T-cell hybridoma cells (α3A3) were infected with retrovirus encoding MS4a4B or with an MIGR vector control. GFP⁺ infected cells were FACS sorted and stimulated with graded amounts of antigen (moth cytochrome C [MCC] peptide) presented by antigen-presenting cells (APCs). Supernatants were harvested after 24 hours, and IL-2 production was measured by CTLL-2 bioassay. The data are representative of 4 independent experiments, and points are averages and SDs of quadruplicate wells. (B) Primary CD4⁺ mouse T-cell blasts were infected with retrovirus-encoding MS4a4B or with a MIGR vector control. Cells were restimulated with PMA and ionomycin in the presence of monensin for 4 hours, and cytokine production was determined by intracellular cytokine staining in GFP⁺ cells using flow cytometry. The data represent the percentage of GFP⁺ cells that were cytokine positive. The results shown are the averages plus SE of 4 separate experiments. ^*Significantly different from vector control (P < .05).