Role of LAIR-1 and CD300 Family Receptors in Regulating Inflammation

我们在B6背景下建立了LAIR-1-/-小鼠，用于研究LAIR-1的体内功能。淋巴器官的表型分析表明，LAIR-1+/+和LAIR-1-/-动物之间没有太大的差异。我们观察到LAIR-1-/-小鼠的脾B细胞百分比略有增加，同时T细胞减少，主要是由于CD8T细胞的减少。这可能不是由于T淋巴细胞的异常运输所致，因为LAIR-1+/+和LAIR-1-/-T细胞同等地运输到外周淋巴器官。在肠道中，我们观察到LAIR-1-/-小鼠的T细胞略有增加，同时NKG2D表达增加。体外实验表明，OT-II LAIR-1-/-CD4T细胞与负载OT-II OVA多肽的APC共同培养时，其增殖能力低于OT-II LAIR-1+/+CD4T细胞。为了研究体内的免疫反应，我们用TNP-OVA免疫动物，发现LAIR-1-/-小鼠的类别转换受到影响。这些动物产生较低水平的IgG2a和IgG2b，而转换为IgG1不受影响。通过使用T细胞特异性LAIR-1-/-动物(CD4CRE LAIR-1FLOX/FLOX)，我们证实类别转换中的缺陷是T细胞特异性的。以前的研究人员已经发表了小鼠B细胞不表达LAIR-1；然而，最近我们发现边缘带B细胞表达LAIR-1。其他初步结果表明，在LAIR-1-/-小鼠中，在化学性腹膜炎模型中，巨噬细胞和嗜酸性粒细胞在腹膜中的募集发生了显著变化，这表明LAIR-1在这些细胞类型向炎症部位运输方面发挥了作用。 我们发现人外周血中的中性粒细胞表达CD300a。为了研究中性粒细胞发育过程中的表达，我们使用了HL-60分化模型。我们发现CD300a的表达是在发育过程中获得的，当中性粒细胞受到内毒素和GM-CSF刺激时，细胞表面的表达非常迅速地增加。这种增加是细胞内受体池移位到细胞表面的结果。CD300a的这种现成的可获得性让人想起CTLA-4，并表明CD300a在调节中性粒细胞反应中可能发挥重要作用。CD300a与含有CD32a(FcRIIa)激活受体的ITAM共连接可抑制CD32a介导的信号转导，但不抑制Toll样受体(TLR)-4介导的ROS的产生。因此，至少对于人中性粒细胞来说，CD300a受体介导的抑制信号在其作用中可能是选择性的。

We have generated LAIR-1 -/- mice on a B6 background to study the in vivo function of LAIR-1. Phenotypic analysis of lymphoid organs did not show large differences between LAIR-1 +/+ and LAIR-1 -/- animals. We have observed a slight increase in the percentage of splenic B cells in the LAIR-1 -/- mice, along with a decrease in T cells, mostly because of a decrease in CD8 T cells. This probably does not result from abnormal trafficking of T lymphocytes, since LAIR-1 +/+ and LAIR-1 -/- T cells traffic equally to peripheral lymphoid organs. In the gut we have observed a slight increase of T cells in the LAIR-1 -/- mice, along with an increase in the NKG2D expression. In vitro experiments showed that OT-II LAIR-1-/- CD4 T cells proliferated less than the OT-II LAIR-1+/+ CD4 T cells when they are cultured with APC loaded with OT-II OVA peptide. To study the immune response in vivo, we have immunized the animals with TNP-OVA and found that class switching is affected in LAIR-1 -/- mice. These animals produced lower levels of IgG2a and IgG2b, while switching to IgG1 is not affected. By using T cell specific LAIR-1 -/- animals (CD4 Cre LAIR-1flox/flox), we confirmed that the defect in class switching is T cell specific. Previous investigators have published that mouse B cells do not express LAIR-1; however, recently we have found that marginal zone B cells are positive for LAIR-1 expression. Other preliminary results have shown that in the LAIR-1 -/- mice there are significant alterations in the recruitment of macrophages and eosinophils into the peritoneum in a model of chemical peritonitis, suggesting a role for LAIR-1 in the trafficking of these cell types towards sites of inflammation. We showed that human neutrophils from peripheral blood express CD300a. To study expression during neutrophil development, we used the HL-60 differentiation model. We showed that CD300a expression is acquired during development and that cell surface expression increases very rapidly when neutrophils are stimulated with LPS and GM-CSF. This increase is the result of translocation of an intracellular pool of the receptor to the cell surface. This ready availability of CD300a is reminiscent of CTLA-4 and suggests that CD300a could play an important role in modulating neutrophil responses. Co-ligation of CD300a with the ITAM containing CD32a (FcRIIa) activation receptor inhibited CD32a mediated signaling, whereas it did not inhibit toll-like receptor (TLR)-4 mediated reactive oxygen species (ROS) production. Therefore, at least for human neutrophils, it seems that the inhibitory signals mediated by the CD300a receptor may be selective in their action.