Characterization of human lymphocytes separated from fetal liver and spleen at different stages of ontogeny

Monitoring C3aR Expression Using a Floxed tdTomato-C3aR Reporter Knock-in Mouse

C3a exerts multiple biologic functions through activation of its cognate C3a receptor. C3^-/- and C3aR^-/- mice have been instrumental in defining important roles of the C3a/C3aR axis in the regulation of acute and chronic inflammatory diseases, including ischemia/reperfusion injury, allergic asthma, autoimmune nephritis, and rheumatoid arthritis. Surprisingly little is known about C3aR expression and function in immune and stromal cells. To close this gap, we generated a floxed tandem-dye Tomato (tdTomato)-C3aR reporter knock-in mouse, which we used to monitor C3aR expression in cells residing in the lung, airways, lamina propria (LP) of the small intestine, brain, visceral adipose tissue, bone marrow (BM), spleen, and the circulation. We found a strong expression of tdTomato-C3aR in the brain, lung, LP, and visceral adipose tissue, whereas it was minor in the spleen, blood, BM, and the airways. Most macrophage and eosinophil populations were tdTomato-C3aR⁺ Interestingly, most tissue eosinophils and some macrophage populations expressed C3aR intracellularly. BM-derived dendritic cells (DCs), lung-resident cluster of differentiation (CD) 11b⁺ conventional DCs (cDCs) and monocyte-derived DCs, LP CD103⁺, and CD11b⁺ cDCs but not pulmonary CD103⁺ cDCs and splenic DCs were tdTomato-C3aR⁺ Surprisingly, neither BM, blood, lung neutrophils, nor mast cells expressed C3aR. Similarly, all lymphoid-derived cells were tdTomato-C3aR^-, except some LP-derived type 3 innate lymphoid cells. Pulmonary and LP-derived epithelial cells expressed at best minor levels of C3aR. In summary, we provide novel insights into the expression pattern of C3aR in mice. The floxed C3aR knock-in mouse will help to reliably track and conditionally delete C3aR expression in experimental models of inflammation.

Novel insights into the expression pattern of anaphylatoxin receptors in mice and men

The anaphylatoxins (AT) C3a and C5a play important roles as mediators of inflammation. Further, they regulate and control multiple innate and adaptive immune responses through binding and activation of their cognate G protein-coupled receptors, i.e. C3a receptor (C3aR), C5a receptor 1 (C5aR1) and C5a receptor 2 (C5aR2), although the latter lacks important sequence motifs for G protein-coupling. Based on their pleiotropic functions, they contribute not only to tissue homeostasis but drive, perpetuate and resolve immune responses in many inflammatory diseases including infections, malignancies, autoimmune as well as allergic diseases. During the past few years, transcriptome expression data provided detailed insights into AT receptor tissue mRNA expression. In contrast, our understanding of cellular AT receptor expression in human and mouse tissues under steady and inflammatory conditions is still sketchy. Ligand binding studies, flow cytometric and immunohistochemical analyses convincingly demonstrated tissue-specific C5aR1 expression in various cells of myeloid origin. However, a detailed map for C3aR or C5aR2 expression in human or mouse tissue cells is still lacking. Also, reports about AT expression in lymphoid cells is still controversial. To understand the multiple roles of the ATs in the innate and adaptive immune networks, a detailed understanding of their receptor expression in health and disease is required. Recent findings obtained with novel GFP or tdTomato AT-receptor knock-in mice provide detailed insights into their expression pattern in tissue immune and stroma cells. Here, we will provide an update about our current knowledge of AT receptor expression pattern in humans and mice.

Multicolor flow cytometric analysis of the CD45 antigen provides improved lymphoid cell discrimination in bone marrow and tissue biopsies

Samples from bone marrow or non-hematopoietic tissue such as solid organ biopsies often contain an excess of non-leukocytes exhibiting lymphocyte-like light scatter characteristics, making it sometimes difficult to define satisfactory light scatter lymphocyte gates. To circumvent this, we describe here a multiparametric method of identifying lymphoid cells by expression of the CD45 antigen, in conjunction with light scatter parameters. A 'third color'-conjugated anti-CD45 antibody was included with every FITC/PE double staining, thereby permitting live or list mode analysis gating on CD45 positive cells. The triple-staining technique was applied to (a) human bone marrow, showing that special attention has to be given to the enumeration of B cells, and (b) to liver biopsies, where gating on CD45 fluorescence and orthogonal light scatter was shown to clearly resolve all lymphocyte subsets from debris. All cell types examined in tissue biopsies as well as T and NK cells in bone marrow were best distinguished by gating on bright CD45 expression in conjunction with low orthogonal light scatter, while accurate identification of marrow B cells relied upon including all levels of CD45 intensity. The multicolor gating procedure, aimed mainly at immune-monitoring of non-malignant tissues, is applicable to most kinds of single cell samples, and may prove to be an aid for lymphocyte gating in cases where leukocyte populations are not clearly resolved on a light scatter basis alone.

Phenotypic characteristics of lymphoid populations of middle gestation human fetal liver, spleen and thymus

Mononuclear cells isolated from liver, spleen and thymus of fetuses between 18 and 24 weeks gestational age were stained for a number of lymphoid cell markers by indirect immunofluorescence and analyzed by flow cytometry. Studies were carried out on freshly isolated mononuclear cell preparations and on cultured cells after selective expansion in interleukin 2 (IL2). Many mononuclear cells in fresh isolates of liver and spleen could not be identified with antibodies to mature T- and B-cell markers. An average of 3% of isolated liver cells and 34% of isolated spleen cells stained positively for CD3, and 19% of liver cells and 37% of spleen cells stained positively for CD20. Lymphoid cells of the fetal thymus were an average 67% CD3+, 76% CD4+, 84% CD8+, and showed greater CD45RO staining (93%) than mononuclear cells of other tissues. Propagation of liver and spleen cell populations in culture favored CD3 phenotypes and CD8 phenotypes. Propagated T cell populations of liver and spleen were primarily TCR alpha/beta+ (81% in liver, 85% in spleen), suggesting a selective advantage in IL2 expansion of alpha/beta T cells over gamma/delta T cells. Propagated gamma/delta T cells of liver and spleen were predominantly TCR gamma/delta 2+. Whereas propagated cells of liver and spleen consisted of approximately 10% gamma/delta+ cells, thymus-derived cells expanded in culture were only an average of 2% TCR gamma/delta+, demonstrating a rarity of IL2-responsive gamma/delta T cells in middle gestation fetal thymus.

An anti-lipid A antibody obtained from the human fetal repertoire is encoded by VH6-V lambda 1 genes

The human hybridoma cell line CB-201 has been obtained from a fusion of fetal spleen lymphocytes (31st gestational week) with heteromyeloma cells. The IgM (lambda) secreted was found to bind to lipid A, whereas other endogenous and exogenous antigens were not recognized. The CB-201 antibody is encoded by the unmutated VH6 gene recombined with DN4 and JH3 elements and a V lambda subgroup 1 gene. Therefore, a VH gene, which was previously described to be over-represented in the fetal repertoire and to be expressed in autoantibody-producing B cells, may encode an anti-bacterial specificity.

In vitro stimulation of human fetal lymphocytes by mitogens and interleukins

Human lymphocytes derived from fetal spleen and liver were studied for their capacity to respond to mitogens and interleukins using different in vitro models (cell volume increase, [3H]thymidine incorporation, Ig secretion). Although the number of mature B and T cells in the fetal liver preparations remained nearly constant [Settmacher et al. (1991) Immunobiol. 182, 256], only lymphocytes obtained from fetal organisms before the 25th week of gestation could respond to some of the polyclonal stimulators (PWM, anti-CD3 + IL-2, SAC + IL-2, SAC + IL-4) tested, whereas cells obtained after that period failed. In the fetal spleen, however, with increasing percentages of mature B and T cells during fetal development, a growing ability to respond to mitogens was registered, which, however, did not achieve the values found for the adult spleen material.