We have observed locally in 3 independent animal houses that OT-I TCR Transgenics on a RAG sufficient background had increased cellularity in absence of Ovalbumin immunisation. CD44/CD62L labeling did not show significantly higher % of activated T cells.
Has anyone else seen this and could share some views on how to explain this observation ?
Is it seen in other TCR Tg backgrounds ?
Thanks in advance for the insight,
Which background are your mice? When you say "increased", what are you comparing it to? Different genetic backgrounds can alter a lot the size and cellularity of secondary an tertiary lymphoid organs. I have seen quite a wide variation in the mesenteric LNs and Peyer's patches, also depending on the sterility/clean condition of your mouse room/facilities.
We brought OT-I (C57 background) from the Jackson Laboratory and bred them in two different animal facilities: in one of them the animals were maintained in SPF conditions and in the other one they were housed in ventilated racks but the food was not irradiated and the cage changes were not done in sterile conditions. The animals bred in the later animal facility developed enlarged mesenteric lymph nodes in a while. The SPF animals always had normal size LNs. So, I think it may be mainly related to the sterility of food and water and also to the sterility of the environment.
I see, that is very likely the reason why you observe such a difference. The "SPF" category and requirements can also vary quite a bit within institutions and facilities. It is very probable that it is simply your mice's gut microbiota what is inducing such a change. You can pretty much assume that mice coming from the Jackson Lab are going to come from the cleanest conditions possible. At least that is my opinion. Especially regarding presence of segmented filamentous bacteria, critical for the development of the gut's immune system and Th17 cells. Good luck!
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