Interspecies variations in the processes of B-cell development and repertoire generation contrast with the greater consistency of T-cell development. B-cell development in mice and humans, with postnatal B-cell generation of new repertoire in the bone marrow throughout life, is regarded as the 'standard' pattern. In contrast, accounts of B cells in birds, sheep, cattle, rabbits and pigs (the 'other' species) describe cessation of gene diversification in the perinatal period, with the gut-associated lymphoid tissue (GALT) functioning as the primary lymphoid organ thereafter. It has become customary to regard the developmental pathways of T and B cells within any individual species as being as dissimilar as the functions of the two mature cell types. Reinterpretation of B-cell development patterns in different species is overdue in response to two types of reports. The first of these describe T-B 'crossover', specifically the intrathymic production of B cells and the extrathymic production of T cells. The second attests to the extent of sharing of B-cell developmental features across the two groups of species. We propose that, as is a feature of other haematopoietic cells, a menu of alternative B- and T-cell pathways has been retained and shared across species. A single pathway usually predominates in any species, masking alternatives. The observed predominance of any pathway is determined by factors such as placental permeability, extent of maturation of the immune system by birth and the feasibility of direct experimental intervention in development.
The first stage in Peyer's patch development in the fetal lamb is characterized by the colonization of the rudimentary Peyer's patches by precursor cells expressing the IgM surface receptor. In the fetal lamb, the spleen has been implicated as the source of gene-rearranged IgM(+) B lymphocytes. This study was intended to quantitate IgM(+) lymphocytes in the spleen, lymph nodes and liver of fetal lambs at various gestational ages between 63 and 110 days using flow cytometry. Flow-cytometric analysis revealed that IgM(+) lymphocytes were rare in the liver being consistently less than 1% at every gestational age examined. IgM(+) lymphocytes were detected in the spleen (mean 9.18%) and prescapular lymph nodes (mean 11.89%) as early as 63 days. In both spleen and lymph nodes, the highest representation of IgM(+) lymphocytes occurred between 70 and 86 days gestation. The highest mean percentage of IgM(+) lymphocytes was observed in the spleen (22.63%) and lymph nodes (17.02%) at 75 days gestation. From 98 days onwards, B-lymphocyte density gradually decreased in both spleen and prescapular lymph nodes. This study indicates that substantial populations of IgM(+) lymphocytes were present in both the spleen and prescapular lymph nodes from 70 days gestation and implies that both of these locations could be potential sources for the normal colonization of the ileal Peyer's patches.
Peripheral blood stem cells (PBSC) mobilised with growth factor with or without chemotherapeutic regimens, are used increasingly in both autologous and allogeneic transplantation. Previously, many PBSC harvests are used directly without ex vivo manipulation, and these PBSC have been shown to be contaminated with tumour cells, which may contribute to subsequent relapses post transplantation. Therefore, requirement for purging of malignant cells from the harvest has initiated the use of various methods to reduce tumour cell contamination of the graft by the positive selection of CD34+ progenitor cells or negative selection of tumour cells using other cell-specific antigens. We report here our local experience with the CliniMACS (magnetic-activated cell separation system) in eight adult patients with haematologic malignancies.
The bursa of Fabricius is critical for B cell development and differentiation in chick embryos. This study describes the production in vitro, from dissociated cell suspensions, of cellular agglomerates with functional similarities to the chicken bursa. Co-cultivation of epithelial and lymphoid cells obtained from embryos at the appropriate developmental stage regularly led to agglomerate formation within 48 hours. These agglomerates resembled bursal tissue in having lymphoid clusters overlaid by well organized epithelium. Whereas lymphocytes within agglomerates were predominantly Bu-1a(+), a majority of those emigrating onto the supporting membrane were Bu-1a(-) and IgM(+). Both agglomerates and emigrant cells expressed activation-induced deaminase with levels increasing after 24 hours. Emigrating cells were actively proliferating at a rate in excess of both the starting cell population and the population of cells remaining in agglomerates. The potential usefulness of this system for investigating the response of bursal tissue to avian Newcastle disease virus (strain AF2240) was examined.