Correlation between FCGR3B CN and protein expression in a family. (A) Array of gene expression patterns (mRNA) for FCGR genes in neutrophils and monocytes of individuals with SLE. Each row corresponds to a gene, and each column to an individual. Red indicates increased expression compared with PBMC reference; green represents reduced expression. The patient (A in panel B) with no FCGR3B expression is marked with an asterisk. (B) Family tree of the FCGR3B-deficient patient A, showing Mendelian inheritance of the null allele. CN was determined using flow cytometry. (C) Flow cytometry of neutrophils stained for PE-labeled antibody to FcγRIIIb demonstrates reduced surface expression on cells from individuals B, C, and D (with a single FCGR3B copy) compared with individuals E and F, who have two FCGR3B copies. Geometric mean fluorescences were 7, 2,265, 2,241, 2,303, 3,484, and 3,730 for A–F, respectively. (D) Gene dosage of FCGR3B relative to CD36, determined by qPCR, for patient A (no FCGR3B), her daughter patient B, her son patient C, and her brother patient D (with a single FCGR3B copy), as well as for her husband patient E and her other brother patient F (with two copies of FCGR3B). (E) qPCR was performed on DNA from all family members whose FcγRIIIb expression had been determined by flow cytometry. Gene dosages of FCGR3B relative to CD36 (by qPCR) were significantly higher in those individuals who by flow cytometry were shown to have greater surface expression of FcγRIIIb. The horizontal bar indicates the mean. (F) Delineation of the extent of the deletion in patient A and family members B, C, and E using PCR; FCGR3B, HSPA7, and FCGR2C are absent. (G) A similar delineation using flow cytometry in patient A. FcγRIIa (neutrophils), FcγRIIb (neutrophils shown, confirmed on B cells, and not depicted) and FcγRIIIa (NK cells) are present (isotype control shaded gray), but FcγRIIIb (neutrophils) is absent. CD59 is expressed on neutrophils, thus GPI linkage is intact.