Bocek P, Dráberová L, Dráber P, Pecht I
Department of Chemical Immunology, Weizmann Institute of Science, Rehovot, Israel.
Eur J Immunol. 1995 Oct;25(10):2948-55. doi: 10.1002/eji.1830251035.
A novel rat basophilic leukemia (RBL) 2H3 subline of rat mucosal mast cells deficient in the expression of the gamma chain (RBL-gamma-) has permitted functional characterization of their low-affinity Fc gamma receptors (Fc gamma R). A rat Fc gamma RII analog of the mouse b2 isoform has been earlier identified and its transcript detected in RBL-2H3 cells. We have noew isolated and sequenced the rat Fc gamma RIIb1 isoform and observed differences between its expression in RBL-2H3 and RBL-gamma-. Furthermore, we demonstrate that rat mucosal mast cells express a second, low-affinity Fc gamma receptor, namely the Fc gamma RIII. Stimulation of either cell line with IgG complexes decreased the expression of transcripts for all Fc gamma R. Hence, ligation of Fc gamma R on rat mucosal mast cells apparently regulate their transcription. Selective stimulation through the Fc gamma RII or Fc gamma RII/III systems, respectively, was accomplished by either using RBL-gamma- line or by saturating the Fc epsilon RI on RBL-2H3 with monomeric IgE. RBL-gamma-cells, which do carry Fc gamma RII (but lack Fc epsilon RI and Fc gamma RIII), do not respond to IgG (and IgE) immune complexes as monitored by specific protein tyrosine phosphorylation, degranulation or cytokine secretion. This finding, together with the restoration of the functional phenotype of parental cells upon gamma chain cDNA transfection into RBL-gamma- cells, unequivocally excludes the possible stimulation of rat mucosal mast cells by clustering of their Fc gamma RII. Fc epsilon RI saturation by IgE on parental RBL-2H3 cells completely blocks their response to IgG immune complexes. Thus the Fc gamma R on these cells do not trigger degranulation and this is not due to the absence of Fc gamma RIII as previously suggested. Therefore, co-clustering of Fc gamma RII and Fc gamma RIII on rat mucosal mast cells does not seem to stimulate them. A possible inhibitory role of Fc gamma RII in this process is suggested and discussed.
一种新型大鼠黏膜肥大细胞的大鼠嗜碱性粒细胞白血病（RBL）2H3亚系，其γ链表达缺失（RBL-γ-），这使得对其低亲和力Fcγ受体（FcγR）进行功能特性分析成为可能。一种小鼠b2亚型的大鼠FcγRII类似物此前已被鉴定，其转录本在RBL-2H3细胞中被检测到。我们现已分离并测序了大鼠FcγRIIb1亚型，并观察到其在RBL-2H3和RBL-γ-中的表达差异。此外，我们证明大鼠黏膜肥大细胞表达第二种低亲和力Fcγ受体，即FcγRIII。用IgG复合物刺激任一细胞系都会降低所有FcγR转录本的表达。因此，大鼠黏膜肥大细胞上FcγR的结合显然调节其转录。分别通过使用RBL-γ-细胞系或用单体IgE使RBL-2H3上的FcεRI饱和，可分别通过FcγRII或FcγRII/III系统进行选择性刺激。RBL-γ-细胞确实携带FcγRII（但缺乏FcεRI和FcγRIII），通过特异性蛋白酪氨酸磷酸化、脱颗粒或细胞因子分泌监测，其对IgG（和IgE）免疫复合物无反应。这一发现，连同将γ链cDNA转染到RBL-γ-细胞后亲代细胞功能表型的恢复，明确排除了大鼠黏膜肥大细胞通过其FcγRII聚集而可能受到刺激的情况。亲代RBL-2H3细胞上IgE使FcεRI饱和完全阻断了它们对IgG免疫复合物的反应。因此，这些细胞上的FcγR不会触发脱颗粒，这并非如先前所认为的是由于缺乏FcγRIII。所以，大鼠黏膜肥大细胞上FcγRII和FcγRIII的共聚集似乎不会刺激它们。文中提出并讨论了FcγRII在此过程中可能的抑制作用。
