Monocytoid B cells: an enigmatic B cell subset showing evidence of extrafollicular immunoglobulin gene somatic hypermutation.

Monocytoid B cells are IgM(+) , IgD(-/+) , CD27(-) B cells, localized in the perisinusoidal area of the lymph node. These cells are especially prominent in infections such as those caused by toxoplasma and HIV. The ontogeny of monocytoid B cells with respect to B cell maturation is incompletely known. We analysed clonal expansion, somatic hypermutation and expression of activation-induced cytidine deaminase (AID) in monocytoid B cells. Sequence analysis of the rearranged immunoglobulin heavy chain genes amplified from microdissected monocytoid B cell zones with a high proportion of proliferating cells reveals the presence of multiple clones with low-level ongoing mutations (mean frequency: 0.46 × 10(-2) per bp). Mutation analysis of these ongoing mutations reveals strand bias, a preference of transitions over transversions as well as the occurrence of small deletions, as observed for somatically mutated immunoglobulin genes in the human germinal centre. Proliferation, ongoing mutation as well as expression of AID, combined, is evidence that monocytoid B cells acquire the mutations in the extrafollicular perisinusoidal area of the lymph node and pleads against a postgerminal centre B cell origin.

Stromal gene signatures in large-B-cell lymphomas.

BACKGROUND: The addition of rituximab to combination chemotherapy with cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP), or R-CHOP, has significantly improved the survival of patients with diffuse large-B-cell lymphoma. Whether gene-expression signatures correlate with survival after treatment of diffuse large-B-cell lymphoma is unclear. METHODS: We profiled gene expression in pretreatment biopsy specimens from 181 patients with diffuse large-B-cell lymphoma who received CHOP and 233 patients with this disease who received R-CHOP. A multivariate gene-expression-based survival-predictor model derived from a training group was tested in a validation group. RESULTS: A multivariate model created from three gene-expression signatures--termed "germinal-center B-cell," "stromal-1," and "stromal-2"--predicted survival both in patients who received CHOP and patients who received R-CHOP. The prognostically favorable stromal-1 signature reflected extracellular-matrix deposition and histiocytic infiltration. By contrast, the prognostically unfavorable stromal-2 signature reflected tumor blood-vessel density. CONCLUSIONS: Survival after treatment of diffuse large-B-cell lymphoma is influenced by differences in immune cells, fibrosis, and angiogenesis in the tumor microenvironment.

Evidence for independent control at the mRNA and protein levels of cellular retinol binding protein 1 in rat Sertoli cells.

Cellular retinol binding protein 1 (CRBP1) is the cytosolic carrier for retinol. It is expressed in many tissues, but the concentrations vary considerably. In Sertoli cells from immature rat testis, CRBP1 is highly expressed. The results of the present study show that regulation of CRBP1 expression at the protein level appears to be independent of regulation at the mRNA level. In Sertoli cells from prepubertal 19-day-old rats, CRBP1 mRNA is strongly induced for up to 72 h by the presence of serum factors. In contrast, treatment of the cells with cAMP analogues led to a rapid reduction in mRNA to quantities less than 5% of control values. However, the changes in CRBP1 mRNA did not lead to similar changes in the concentration of CRBP1 protein during 72 h of observation. Similarly, treatment of cells from 32- and 44-day-old rats with serum led to increased CRBP1 mRNA, whereas cAMP treatment resulted in a decrease in CRBP1 mRNA. Again, no changes were observed in the concentration of CRBP1 protein. Furthermore, co-incubation of Sertoli cells from 19-day-old rats with purified pachytene spermatocytes or round spermatids resulted in an increase in mRNA for CRBP1. However, comparable changes in CRBP1 protein concentrations were not observed. Neither cAMP nor serum changed the fraction of CRBP1 mRNA that was associated with polysomes. As a possible explanation for some of the results, pulse-chase experiments showed that the rate of CRBP1 degradation in cultured Sertoli cells is decreased by cAMP. It is proposed that these changes at the level of protein turnover contribute to the maintenance of stable concentrations of CRBP1 even when the corresponding mRNA concentrations vary markedly.

The effect of retinoids and clofibric acid on the peroxisomal oxidation of palmitic acid and of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid in rat and rabbit hepatocytes.

The effects of retinoids and the peroxisome proliferator clofibric acid on peroxisomal enzyme pathways were studied in hepatocytes from both rat and rabbit. Retinoic acid and retinol increased the activity of acyl-CoA oxidase in rabbit hepatocytes around 60% and around 30% in rat hepatocytes. Exposure to clofibric acid caused an increase in acyl-CoA oxidase activity of 115% in rat hepatocytes and of 40% in rabbit hepatocytes, indicating that rabbit is less sensitive to peroxisome proliferator than rat. Simultaneous exposure to clofibric acid and retinoids did not act additatively or synergistically. Both rabbit and rat hepatocytes expressed mRNA for the peroxisome proliferator activated receptor, (PPAR), although the transcript in rabbit was slightly smaller compared to that expressed in rat hepatocytes. The effect of retinoic acid in 7800 C1 Morris rat hepatoma cells, a cell line known to have an inducible peroxisomal beta-oxidation of fatty acids, was only slight with an increase of the acyl-CoA oxidase activity of 25% compared with control cells. As for clofibric acid, which gave a 2-fold induction of the acyl-CoA oxidase activity, the effect of retinoic acid was potentiated by dexamethasone. These cells also expressed mRNA for PPAR, with the same size as that found in rat hepatocytes. The oxidation of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid (THCA), an intermediate in bile acid formation, in rat hepatocytes increased 110% by clofibric acid and around 80% by retinoic acid. In rabbit hepatocytes, clofibric acid increased the oxidation rate 75% and retinoic acid 100%. The results presented here show similarities in the effects of retinoids and clofibric acid on the acyl-CoA oxidase activity and the oxidation rate of THCA, since they increase these two peroxisomal activities in hepatocytes in vitro. A decrease in both these enzyme activities occurs during cultivation time in untreated primary hepatocyte cultures. The present data may therefore either be explained by an increased expression or an induced stability of the enzymes involved.