Genomic Composition of Howell-Jolly Bodies.

Erythrocyte inclusion bodies that are now commonly referred to as Howell-Jolly Bodies (HJB) were originally discovered over 100 years ago by microscopy. These nuclear fragments are observed in the erythrocytes of patients lacking splenic function, but their precise genomic origins are vague. Here we report studies of the genetic content of HJB using a molecular cytogenetic method known as Comparative Genomic Hybridization (CGH). Peripheral blood samples from six splenectomized human donors were studied. All donors had undergone splenectomies prior to this study for diagnostic and therapeutic indications related to underlying neoplastic and autoimmune disease. Ultrasound testing was used to rule out the presence of accessory splenic tissue, and peripheral blood smears confirmed the presence of HJB. Nucleated cells were removed by density gradients and leukocyte filtration for use as patient-matched controls. DNA was isolated from the leukocytes and HJB-containing erythrocytes. The presence of high molecular weight HJB DNA was confirmed in each sample using gel electrophoresis. As expected, it was not possible to obtain sufficient quantities of DNA from the control erythrocytes of healthy individuals with normal splenic function. CGH was performed using equivalent amounts of reference genomic DNA co-hybridized with HJB DNA or matched donor leukocyte DNA. Agilent oligonucleotide CGH arrays were hybridized and scanned according to the manufacturer’s instructions. The control hybridizations (genomic DNA isolated from donor leukocytes) demonstrated standard patterns consistent with the donor’s karyotype. In contrast, the HJB hybridization signals demonstrated an unusual pattern of centromeric-to-telomeric enrichment on each chromatid of each chromosome. The HJB hybridization signals also increased as a function of distance from the centromere according to the chromatid size. The enhanced signal relative to centromeric distance varied considerably between chromosomes, but was remarkably consistent between donors. These data suggest Howell-Jolly Bodies contain a non-random distribution of centromere-depleted chromatin generated after DNA double-strand breakage during erythroid differentiation.