This is very interesting study from Journal of Immunology (JI). Here, researcher led by Timothy Hand at the University of Pittsburgh Medical School, showed that CBir1 transgenic T cells, thought to cause gut inflammation by recognizing flagellin expressing microbiota, were in fact specific for non-flagellin antigens.
CBir1 transgenic mouse have been used for past 10 years to model human Crohn's disease in mice. CBir1 tetramer+ T cells recognize epitope from flagellin, antigen thought to be a target in Crohn's disease. Interestingly, all of those experiments were done using CBir1 T cells on WT background. This could be an issue because it has been known for some time now that transgenic T cells on WT background could use alternative Vα chain to form TCR with new specificity.
To avoid such limitation, here the authors generated CBir1 mouse on RAG KO background that only expressed transgenic Vα:Vβ chains. Surprisingly, unlike CBir1:WT T cells, CBir1:RagKO T cells when transferred in immunodeficient hosts did not induce colitis, and it was not because CBir1:RagKO T cells differentiate into Foxp3+ T cells. It appears that CBir1:RagKO T cells just did not see flagellin epitope in adoptive host.
In vitro tests showed that both CBir1:WT T cells and CBir1:RagKO T cells could respond to DCs pulsed with flagellin epitope [it would have been better and more relevant here to use DCs pulsed with gut flora component].
Other tests showed that CBir1:WT T cells in gut tissue could express alternative Vα chain to form a completely new TCR specificity together with transgenic Vβ chain such as against Ags derived from Helicobacter (HH1713 tetramer).
In summary, it appears that CBir1 T cells initiate colitis by recognizing non-flagellin antigen from the gut flora through non-CBir1 TCR and only following gut inflammation and gut leakage do flagellin-specific CBir1 transgenic T cells get activated and participate in overall colitis.
So, what is missing from this study? One, it would have been relevant to transfer in vitro activated CBir1:RagKO T cells or activate them in vivo directly to see if then they could initiate colitis. Second, the authors could have tried monocolonization of germ-free mice to see the source of non-flagellin microbiota. Third, there is inconsistency between Fig. 3B and Fig. 6A with regard of proliferation of CBir1:WT T cells in response to Vanc-treated samples (in vitro it did not proliferate but in vivo it did).
posted by David Usharauli
In vitro tests showed that both CBir1:WT T cells and CBir1:RagKO T cells could respond to DCs pulsed with flagellin epitope [it would have been better and more relevant here to use DCs pulsed with gut flora component].
Other tests showed that CBir1:WT T cells in gut tissue could express alternative Vα chain to form a completely new TCR specificity together with transgenic Vβ chain such as against Ags derived from Helicobacter (HH1713 tetramer).
In summary, it appears that CBir1 T cells initiate colitis by recognizing non-flagellin antigen from the gut flora through non-CBir1 TCR and only following gut inflammation and gut leakage do flagellin-specific CBir1 transgenic T cells get activated and participate in overall colitis.
So, what is missing from this study? One, it would have been relevant to transfer in vitro activated CBir1:RagKO T cells or activate them in vivo directly to see if then they could initiate colitis. Second, the authors could have tried monocolonization of germ-free mice to see the source of non-flagellin microbiota. Third, there is inconsistency between Fig. 3B and Fig. 6A with regard of proliferation of CBir1:WT T cells in response to Vanc-treated samples (in vitro it did not proliferate but in vivo it did).
posted by David Usharauli
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