BTLA and systemic lupus erythematosus: Moreover, compared to BTLA+ DN B cells, BTLAlow DN B cells from SLE patients express higher levels of CD38 (MFI: 16,470 ± 3652 vs. 6827 ± 806 for BTLA+ cells; p < 0.05) and SLAMF7 (SLAM Family Member 7) (MFI: 2986 ± 385 vs. 1357 ± 111 for BTLA+ cells; p < 0.001)—which are classical markers for plasma cells—and do not express HLA-DR, which is also absent from the plasma cell surface (MFI: 20,740 ± 1395 for BTLA+ B cells vs. 1731 ± 475 for BTLAlow B cells; p <0.001) (Figure 4C).