Distribution of perforin and GM1 in SAP-deficient CD8⁺ T cells. (A) GM1 and perforin distribution in normal and SAP-deficient CD8⁺ T cells (T) forming conjugates with EBV-positive B-cell line JY (B). The effects of blocking anti-2B4 mAbs on normal CD8⁺ T cells are also shown. One representative conjugate is shown in parallel as bright field (i-iii), GM1 staining (iv-vi), and perforin staining (vii-ix). (B) Quantitative analysis of GM1 and perforin coclustering at the area of contact with B-cell targets in T cells from 3 SAP-deficient patients and T cells from 3 healthy donors, either untreated or treated with blocking anti-2B4 mAbs. Cells were considered positive for coclustered GM1 and perforin if the staining was centered at the site of contact with the B cell and occupied less than one third of the cell surface. Data are represented as mean percentages (± SDs) of 3 experiments counting T cells forming clusters with a single JY B-cell target (for each cell line a total of 250-300 cells was counted). Statistical analysis was performed using an unpaired t test, and P values corresponding to the comparison of 1 group with the other are indicated.