Ratcliffe M J, Lassila O, Pink J R, Vainio O
Eur J Immunol. 1986 Feb;16(2):129-33. doi: 10.1002/eji.1830160204.
The avian bursa of Fabricius contains about 1 X 10(4) discrete follicles, each of which is colonized by a small number of lymphoid progenitor cells during embryonic life. We have previously shown (J.R.L. Pink et al., Eur. J. Immunol. 1985. 15:617) that all, or almost all B cell progenitors in the bursae of 4-day-old chicks express cell surface IgM. In this report, we have analyzed the distribution of cell surface (s)IgM-1 allotypes within individual follicles of (M-1a/M-1b) allotype heterozygous birds. Although the majority of follicles contained a mixture of sIgM-1a+ and sIgM-1b+ cells, a significant proportion of isolated follicles contained exclusively sIgM-1a+ or sIgM-1b+ cells. Statistical analysis of the frequency of such "M-1a" and "M-1b" follicles demonstrated that the sIg+ B cells in the bursae of 4-8-week-old birds are derived from 2-4 allotypically committed precursor cells per follicle. Since we have previously shown that each bursal follicle is colonized by 2-5 pre-bursal stem cells, these cells must be committed to the eventual expression of one or other allotypic haplotype before they have undergone extensive proliferation within the bursa. In addition, we show that almost all B progenitor cells from the bursae of chicks which had been allotype suppressed as embryos were committed to synthesis of the nonsuppressed allotype, showing that this commitment was essentially complete at the time of suppression (i.e. before 19 days of incubation). Finally the bone marrow of 16-day embryos was used to reconstitute the bursal lymphocytes of cyclophosphamide-treated host embryos. Reconstitution was inhibited by anti-Ig antiserum indicating that most 16-day embryonic BM-derived bursal cell precursors also express sIgM. These results raise the possibility that expression of sIgM may be controlled by a "biological clock" rather than by any inductive capacity of the bursal microenvironment. Furthermore, these results provide further evidence that in normal birds a self-renewing sIg+ B cell population in the hatched chicken is the sole source of B cells in the adult.
禽类法氏囊包含约1×10⁴个离散的滤泡，在胚胎期每个滤泡由少量淋巴祖细胞定殖。我们之前已经表明（J.R.L. Pink等人，《欧洲免疫学杂志》1985年。15:617），4日龄雏鸡法氏囊中的所有或几乎所有B细胞祖细胞都表达细胞表面IgM。在本报告中，我们分析了（M-1a/M-1b）同种异型杂合禽类个体滤泡内细胞表面（s）IgM-1同种异型的分布。虽然大多数滤泡含有sIgM-1a⁺和sIgM-1b⁺细胞的混合物，但相当比例的单个滤泡仅含有sIgM-1a⁺或sIgM-1b⁺细胞。对这种“M-1a”和“M-1b”滤泡频率的统计分析表明，4至8周龄禽类法氏囊中sIg⁺B细胞源自每个滤泡2至4个同种异型定向的前体细胞。由于我们之前已经表明每个法氏囊滤泡由2至5个法氏囊前体细胞定殖，这些细胞在法氏囊内进行广泛增殖之前必须已定向于最终表达一种或另一种同种异型单倍型。此外，我们表明，几乎所有来自胚胎期被同种异型抑制的雏鸡法氏囊的B祖细胞都定向于合成未被抑制的同种异型，这表明这种定向在抑制时（即孵化19天之前）基本完成。最后，用16日龄胚胎的骨髓重建经环磷酰胺处理的宿主胚胎的法氏囊淋巴细胞。抗Ig抗血清抑制了重建，表明大多数16日龄胚胎骨髓来源的法氏囊细胞前体也表达sIgM。这些结果提出了sIgM的表达可能由“生物钟”控制而非法氏囊微环境的任何诱导能力控制的可能性。此外，这些结果进一步证明，在正常禽类中，孵化后的鸡体内自我更新的sIg⁺B细胞群体是成体中B细胞的唯一来源。
