MHC expression in nonlymphoid tissues of the developing embryo: strongest class I or class II expression in separate populations of potential antigen-presenting cells in the skin, lung, gut, and inter-organ connective tissue

Identification of qPCR reference genes suitable for normalising gene expression in the developing mouse embryo

Background: Progression through mammalian embryogenesis involves many interacting cell types and multiple differentiating cell lineages. Quantitative polymerase chain reaction (qPCR) analysis of gene expression in the developing embryo is a valuable tool for deciphering these processes, but normalisation to stably-expressed reference genes is essential for such analyses. Gene expression patterns change globally and dramatically as embryonic development proceeds, rendering identification of consistently appropriate reference genes challenging. Methods: We have investigated expression stability in mouse embryos from mid to late gestation (E11.5-E18.5), both at the whole-embryo level, and within the head and forelimb specifically, using 15 candidate reference genes ( ACTB, 18S, SDHA, GAPDH, HTATSF1, CDC40, RPL13A, CSNK2A2, AP3D1, HPRT1, CYC1, EIF4A, UBC, B2M and PAK1IP1), and four complementary algorithms (geNorm, Normfinder, Bestkeeper and deltaCt). Results: Unexpectedly, all methods suggest that many genes within our candidate panel are acceptable references, though AP3D1, RPL13A and PAK1IP1 are the strongest performing genes overall (scoring highly in whole embryos, heads or forelimbs alone, and in all samples collectively). HPRT1 and B2M are conversely poor choices, and show strong developmental regulation. We further show that normalisation using our three highest-scoring references can reveal subtle patterns of developmental expression even in genes ostensibly ranked as acceptably stable ( CDC40, HTATSF1). Conclusion: AP3D1, RPL13A and PAK1IP1 represent universally suitable reference genes for expression studies in the E11.5-E18.5 mouse embryo.

Identification of qPCR reference genes suitable for normalising gene expression in the developing mouse embryo

Background: Progression through mammalian embryogenesis involves many interacting cell types and multiple differentiating cell lineages. Quantitative polymerase chain reaction (qPCR) analysis of gene expression in the developing embryo is a valuable tool for deciphering these processes, but normalisation to stably-expressed reference genes is essential for such analyses. Gene expression patterns change globally and dramatically as embryonic development proceeds, rendering identification of consistently appropriate reference genes challenging.

Methods: We have investigated expression stability in mouse embryos from mid to late gestation (E11.5–E18.5), both at the whole-embryo level, and within the head and forelimb specifically, using 15 candidate reference genes ( ACTB, 18S, SDHA, GAPDH, HTATSF1, CDC40, RPL13A, CSNK2A2, AP3D1, HPRT1, CYC1, EIF4A, UBC, B2M and PAK1IP1), and four complementary algorithms (geNorm, Normfinder, Bestkeeper and deltaCt).

Results: Unexpectedly, all methods suggest that many genes within our candidate panel are acceptable references, though AP3D1, RPL13A and PAK1IP1 are the strongest performing genes overall (scoring highly in whole embryos, heads or forelimbs alone, and in all samples collectively). HPRT1 and B2M are conversely poor choices, and show strong developmental regulation. We further show that normalisation using our three highest-scoring references can reveal subtle patterns of developmental expression even in genes ostensibly ranked as acceptably stable ( CDC40, HTATSF1).

Conclusion: AP3D1, RPL13A and PAK1IP1 represent universally suitable reference genes for expression studies in the E11.5-E18.5 mouse embryo.

Stemness Correlates Inversely with MHC Class I Expression in Pediatric Small Round Blue Cell Tumors

Recently, immunotherapeutic approaches have become a feasible option for a subset of pediatric cancer patients. Low MHC class I expression hampers the use of immunotherapies relying on antigen presentation. A well-established stemness score (mRNAsi) was determined using the bulk transcriptomes of 1134 pediatric small round blue cell tumors. Interestingly, MHC class I gene expression (HLA-A/-B/-C) was correlated negatively with mRNAsi throughout all diagnostic entities: neuroblastomas (NB) (n = 88, r = −0.41, p < 0.001), the Ewing’s sarcoma family of tumors (ESFT) (n = 117, r = −0.46, p < 0.001), rhabdomyosarcomas (RMS) (n = 158, r = −0.5, p < 0.001), Wilms tumors (WT) (n = 224, r = −0.39, p < 0.001), and central nervous system-primitive neuroectodermal tumors CNS-PNET (r = −0.49, p < 0.001), with the exception of medulloblastoma (MB) (n = 76, r = −0.24, p = 0.06). The negative correlation of MHC class I and mRNAsi was independent of clinical features in NB, RMS, and WT. In NB and WT, increased MHC class I was correlated negatively with tumor stage. RMS patients with a high expression of MHC class I and abundant CD8 T cells showed a prolonged overall survival (n = 148, p = 0.004). Possibly, low MHC class I expression and stemness in pediatric tumors are remnants of prenatal tumorigenesis from multipotent precursor cells. Further studies are needed to assess the usefulness of stemness and MHC class I as predictive markers.

Islet inflammation and fibrosis in a spontaneous model of type 2 diabetes, the GK rat

The molecular pathways leading to islet fibrosis in diabetes are unknown. Therefore, we studied gene expression in islets of 4-month-old Goto-Kakizaki (GK) and Wistar control rats. Of 71 genes found to be overexpressed in GK islets, 24% belong to extracellular matrix (ECM)/cell adhesion and 34% to inflammatory/immune response families. Based on gene data, we selected several antibodies to study fibrosis development during progression of hyperglycemia by immunohistochemistry. One-month-old GK and Wistar islets appeared to be similar. Two-month-old GK islets were strongly heterogenous in terms of ECM accumulation compared with Wistar islets. GK islet vascularization, labeled by von Willebrand factor, was altered after 1 month of mild hyperglycemia. Numerous macrophages (major histocompatibility complex class II(+) and CD68(+)) and granulocytes were found in/around GK islets. These data demonstrate that marked inflammatory reaction accompanies GK islet fibrosis and suggest that islet alterations in this nonobese model of type 2 diabetes develop in a way reminiscent of microangiopathy.

Robust ability of IFN-gamma to upregulate class II MHC antigen expression in tumor bearing rat brains

T cells are attractive for delivering therapy to brain tumor, especially disseminated micro-tumor. However, to trigger effector function, tumor antigen must be re-presented to T cells, via major histocompatibility complex (MHC) proteins, at the tumor site. In normal brain, MHC+ antigen-presenting cells (APC) are rare, but abundant after gamma interferon (IFN-gamma) injection. Here we studied tumor-bearing brains. IFN-gamma (or buffer) was injected stereotactically into brains with established tumors from a panel of immunologically varied glioma cell lines, some expressing b-galactosidase as a micro-tumor marker. Four days later, cryostat sections were stained for tumor and MHC proteins. In phosphate-buffered saline-injected controls, class II MHC+ potential APC (microglia, macrophages) were seen only at (some) tumor sites. In rats that received IFN-gamma, class II+ potential APC were widespread, including all actual and potential micro-tumor sites and all tumor-free areas. In the same slides, neither class I nor class II MHC antigen was detected in neural cells or most tumor cells. This MHC pattern favors indirect re-presentation of tumor antigen, by tumor-adjacent APC. The robust response to IFN-gamma might also be exploited in other ways: activated microglia and macrophages can attack tumor directly, and class II+ APC may help mark micro-tumor sites.

Does the transplantation process modify the immunogenicity of fetal adrenal grafts in rat?

The concept that fetal tissue transplants enjoy an immunologic privilege grounds on the primary immaturity of major histocompatibility complex (MHC) expression. However, experiences in human organ transplantation reveal that the immunogenicity of any graft could be modified by external factors such as ischemia. Consequently, the question arises, whether the process of transplantation modifies the immunogenicity of fetal grafts. In a syngeneic rat model (Lewis), fetal adrenal glands were transplanted into the greater omentum of adult hosts. After harvesting the grafts sequentially, the immunogenicity was evaluated by analyzing the expression and distribution of the MHC classes I and II and were compared with untreated organs of equivalent age. The untreated fetal adrenal gland depicted little immunogenicity. However, compared with age-matched untreated control organs, at 2 wk after transplantation, the grafts demonstrated an increased expression of MHC I and II, upregulated throughout the entire adrenal cortex. No signs of MHC-mediated rejection were found. The upregulation of MHC persisted until the eighth week after transplantation. At 3 months after transplantation the expression of MHC I and II returned to the normal pattern of untreated controls. As this study used a purely syngeneic model, the immunologic changes observed could not be induced by a graft vs. host incompatibility, instead they were caused by experimental factors. The expressions of MHC class I and II was increased at 2 wk, but these proteins did not induce a T-cell mediated rejection or cellular infiltration. In conclusion, these findings question the concept of an immunologic privilege of fetal tissue transplants. Instead, experimental factors may modify the tissue's primary immaturity of its MHC. Further investigations must evaluate, whether the increase in MHC expression will have an impact on the rejection of fetal adrenal grafts in allogeneic hosts.

Survival of fetal skin grafts is prolonged on the human peripheral blood lymphocyte reconstituted-severe combined immunodeficient mouse/skin allograft model

BACKGROUND

Fetal tissue is considered to be immune privileged and is under extensive investigation as a source of tissue for transplantation. In this paper, we analyzed the immune properties of human fetal and neonatal skin before and after transplantation to severe combined immunodeficient (SCID) mice. Using a human peripheral blood mononuclear cell reconstituted SCID (huPBMC-SCID) mouse model of allograft rejection, we compared the immune response to transplanted fetal and neonatal skin.

METHODS

We analyzed human fetal (55-122 days of gestation) and neonatal skin samples by routine histology and immunohistochemistry for the expression of (MHC class I and II antigens before and after transplantation to SCID mice. After transplantation, we injected the mice with huPBMCs and analyzed the survival of neonatal and fetal skin grafts both visually and microscopically.

RESULTS

We detected no class II expression in fetal skin of all gestational ages and only weak class I expression after 89 days compared with abundant class I and II expression in neonatal skin before transplantation. When transplanted to SCID mice, fetal skin grafts differentiated and expressed class I and II, but the levels were lower than neonatal grafts. In mice injected with huPBMCs, rejection of neonatal grafts started on day 5, and by day 9 all grafts were rejected. In contrast, rejection of fetal skin grafts was significantly delayed. Rejection started on day 13 and was complete by day 23 (P<0.00005). Histology sections from the rejected grafts showed marked CD3+ T cell infiltration in the human skin with a sharp demarcation between the human and mouse skin, with no T-cell infiltration in the mouse skin. CD4+ and CD8+ T cells were present in the rejected sites in similar densities.

CONCLUSIONS

Our results show that fetal skin differentiates and expresses increased amounts of MHC class I and class II antigens when transplanted to SCID mice. However, these levels are much lower than the levels found in neonatal skin. We demonstrate that the survival of human fetal skin allografts is markedly prolonged compared with that of neonatal skin grafts in the huPBMC-SCID mouse model. Our results support the hypothesis that low levels of MHC antigen expression lead to a delay in the rejection of fetal skin and further demonstrate the utility of the huPBMC-SCID mouse model to investigate the molecular and cellular mechanisms of the immune response to human fetal tissues.