Thursday, March 15, 2018

Reduced CTLA-4 signaling predisposes to Th2 driven gastric tumorigenesis

Anti-CTLA4 antibodies such as Yervoy, has been used in clinical practice to treat solid tumors. It supposed to work either by augmenting and revitalizing effector T cells function directly or indirectly through temporal silencing of inhibitory Foxp3+ Treg population or both. However, new study from Journal of Experimental Medicine showed that at least in [genetically predisposed] mice reduced CTLA-4 signaling by itself could cause Th2 driven tumorigenic transformation of stomach epithelial tissue.

For this study the authors created transgenic CTLA4 shRNA knockdown (CTLA4KD) mice on the BALB/c × C57BL/6 (B6) mixed genetic background. This they did because it appears that BALB/c but not B6 mice were susceptible developing gastric tumors in this model. CTLA4KD mice showed gastric epithelial transformation by 20w of age. Similarly, month long treatment of newborn BALB/c mice with anti-CTLA4 antibody also led to gastric epithelial transformation.

This tumorigenic transformation was CD4 T cell dependent and effector T cells from CTLA4KD but not from WT mice could mediate it. It indicated that changes in effector T cell composition and functionality were driving de novo inflammatory tumorigenesis.

Interestingly, gastric epithelial transformation were happening even in germ-free CTLA4KD mice lacking microbiota. However, since these mice also harbor increased numbers of inflammatory T cells, in all subsets analyzed such as Th1, Th2, Th17, and independent of microbiota it could indicate that T cells could be responding to antigens from food or environment.

Finally, elimination of canonical T helper cytokines showed that surprisingly neither IFN-γ nor IL-17 but IL-4 deficiency could abolish gastric epithelial transformation under conditions of reduced CTLA-4 activity.

In summary, this study suggests that inherited or clinically-induced reduction of CTLA-4 signaling in predisposed individuals could paradoxically lead to inflammatory tumorigenesis driven by type II immunity.

posted by David Usharauli

Saturday, March 10, 2018

Translocation of a specific gut pathobiont, Enterococcus gallinarum, exacerbate autoimmune phenotype

A new study in journal Science suggests that a specific gut pathobiont, Enterococcus gallinarum, could exacerbate autoimmune phenotype in predisposed mouse strain. This autoimmune phenotype in mice are thought to represent mouse version of human systemic lupus erythematosus (SLE).

SLE is associated with genetic polymorphism linked to excessive signaling of RNA sensing Toll-like receptor 7 (TLR7) and type I interferons (IFNs). In the specific pathogen-free (NZW × BXSB)F1 hybrid mouse, responses to endogenous retrovirus glycoprotein 70 (ERV gp70) via TLR7 signaling leads to progressive autoimmune response by pathogenic anti-phospholipid [β2-glycoprotein I (β2GPI)] and anti–double-stranded DNA (dsDNA) antibodies.

The authors observed that certain antibiotic treatment significantly improved survival of (NZW × BXSB)F1 hybrid mice.

Further experiments showed that there was bacterial translocation from gut tissue into portal veins and livers in these mice that could be reduced by antibiotic treatment.

16S rRNA sequencing and species-specific PCR consistently revealed Enterococcus gallinarum (E. gallinarum) in the feces, small intestine and liver of (NZW× BXSB)F1 mice. Monocolonzation of germ-free mice with E. gallinarum (EG, here) revealed that it could specifically drive Th17 response, unlike E. faecalis or B. thetaiotaomicron.

Moreover, E. gallinarum could specifically drive  ERV gp70 expression in the liver cells,

and augment anti-nucleic acid antibody response.

Finally, the authors showed that liver tissues from human SLE patients harbored E. gallinarum.

In summary, this study proposes the following patho-mechanism of SLE: when residing in predisposed individuals E. gallinarum causes degradation of gut barrier function, then translocates internally, activates Th17 pathway and initiates "innate" autoimmune phenotype by activating expression of retroviral genes and amplifying endogenous nucleic acid detection system that breaks tolerance checkpoints and leads to auto-antibody formation, Ab-Ag complex deposition in tissues and inflammatory disease exaggeration. The authors proposed antibiotic treatment could provide relieves in certain SLE patients.

However, there are few unanswered questions in this study: first of all, it is clear that E. gallinarum does not induce autoimmunity by itself. Second, If Th17 activity is relevant for E. gallinarum action, then it would have been more valuable for the authors to compare E. gallinarum to segmented filamentous bacteria (SFB) a known inducer of Th17 response in the gut tissue.

posted by David Usharauli

Saturday, March 3, 2018

Specific microbiota species induce serum IgA that protects against sepsis

Some 10 years ago the scientists made observation that microbiota difference between different mouse colonies is responsible for selective TH17 expansion in the gut. Since then, field of immunology was flooded with numerous observations linking gut [and other tissue] microbiota to functional status of immune system.

One such study was recently published in journal Cell Host and Microbe. The researchers observed that serum IgA secreted by bone marrow residing plasma cells (BM PCs) were selectively enriched in mouse colony harboring members of Proteobacteria phylum. More importantly, these serum IgA protected mice during sepsis following gut damage.

Initially, the authors observed that their institute's B6 mouse colony (PENN-SPF) differed from commercial vendor B6 mice in their serum [but not small intestine] IgA status. Co-housing experiment indicated potential involvement of microbiota.

Indeed, 16S ribosomal gene sequencing showed enrichment of Proteobacteria phylum in local mouse colony (and also Deferribacteres).

Serum IgA bound microbiota and sequencing of serum IgA+/IgA- microbiota species confirmed selective enrichment of species within Proteobacteria phylum.

Development of microbiota-specific serum IgA were T cell-dependent.

Finally, serum IgA protected mice against sepsis following gut tissue damage and microbiota invasion (translocation).

In summary, serum IgA, but not intestinal IgA, is produced by bone marrow plasma cells in response to selective microbiota species, mostly from Proteobacteria phylum in mice. These serum IgA could bind microbiota, it developed in a T cell-dependent manner and protected host during gut flora invasion (translocation) in condition such as sepsis. However, it is not clear why serum IgG [in IgA KO mice] could not protect against sepsis in this study since one previous study already showed that serum IgG protected against gram negative bacteria such as E. coli. It is possible that serum IgA and IgG play non-redundant functions by protected against different microbial species.

posted by David Usharauli