Analysis of CD93 Expression in Human Hematolymphoid Cells.
Ila Bansal, Rebecca Owens, John D Shaughnessy, Robert B Lorsbach. University of Arkansas for Medical Sciences, Little Rock; Myeloma Institute for Research and Therapy, Little Rock, AR
Background: CD93 (or C1QR1) is encoded by the C1QR1 gene. In mice, CD93 is expressed during early bone marrow (BM) B-cell differentiation and is down-regulated during subsequent stages of maturation. Recent analysis of mice deficient in CD93 revealed that CD93 is expressed in mature plasma cells (PCs) and is required for maintenance of BM PC numbers and antibody secretion. These findings from murine studies prompted us to evaluate whether CD93 is similarly expressed in human PCs as well as plasma cell myeloma (PCM). We also characterized CD93 expression in other hematopoietic cells types.
Design: BM from 47 cases of PCM and 9 cases of reactive plasmacytosis were evaluated by 4-color flow cytometry (FC). In addition, the expression of CD93 in 5 cases of acute myeloid leukemia (AML) and 4 normal peripheral blood (PB) samples was also evaluated. FC was performed using a FACSCanto II flow cytometer and data analyzed using FACSDiva software. To detect CD93 expression, cell suspensions were incubated with FITC-conjugated anti-CD93 (clone R139, BD Biosciences). In PCMs where gene expression profiling (GEP) was performed, RNA was extracted from CD138 purified PCs and analyzed using an Affymetrix-based platform with hybridization to U133 gene chip microarrays.
Results: Using FC, reactive PCs and PCMs were uniformly CD93- as assessed by FC. To confirm the CD93 negativity, C1QR1 gene expression was also evaluated in PCM cases by GEP. The evaluated PCMs yielded an average C1QR1 mRNA expression level of 281 in these cases, with both C1QR1 gene probe sets present on the Affymetrix U133 gene chips yielding similarly low signals, compared to expression levels of 2700 and 15,086 for the moderately and highly expressed genes CD200 and CD138, respectively. By contrast, normal PB monocytes expressed moderate CD93, whereas granulocytes were only CD93dim by FC. PB lymphocytes were uniformly CD93-. In all analyzed AMLs, the leukemic blasts were CD93-; however, in 2 cases, a significant monocytic population was present and was moderately positive for CD93.
Conclusions: CD93 is not expressed in normal or malignant PCs as assessed by FC, and the C1QR1 gene is only weakly or not expressed in PCM. The differences in CD93 expression between human and mouse PCs may be attributable to species-specific differences in the regulation of expression of the C1QR1 gene. CD93 is expressed by normal PB monocytes and only weakly expressed by granulocytes. Thus, CD93 may serve as a useful lineage-specific marker for benign and malignant cells of the monocyte lineage.
Tuesday, March 1, 2011 1:00 PM
Poster Session IV # 157, Tuesday Afternoon