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Intestinal intraepithelial lymphocytes: identification of an inhibitory subpopulation
D H Teitelbaum1, B C Reyes, R M Merion
1Department of Surgery, University of Michigan Medical Center, Ann Arbor 48109, USA.
Insights
Intestinal intraepithelial lymphocytes (iIEL) inhibit immune responses. The CD8αα+ subpopulation of iIEL is primarily responsible for this suppressive effect, crucial for preventing antigen sensitization.
Area of Science:
- Immunology
- Gastroenterology
Background:
- Intestinal intraepithelial lymphocytes (iIEL) are crucial for maintaining gut homeostasis.
- Their role in preventing overwhelming sensitization to luminal antigens is recognized but not fully understood.
Purpose of the Study:
- To identify the specific subpopulation of iIEL responsible for inhibiting immune proliferation.
- To elucidate the cellular mechanisms underlying iIEL-mediated immune regulation.
Main Methods:
- Mixed lymphocyte cultures (MLC) using rat splenocytes (BN as responder, Lewis as stimulator).
- Addition of whole iIEL or specific iIEL subpopulations (CD45+, CD8+, CD4+, CD8αα+, CD8αβ+) to MLC.
- Proliferation assays measured by counts per minute (CPM).
Main Results:
- Addition of iIEL to MLC significantly reduced proliferation by 59% (P < 0.05).
- Removal of CD45+ cells abolished the inhibitory activity, confirming lymphoid origin.
- Loss of CD8+ cells, but not CD4+ cells, eliminated inhibition.
- The CD8αα+ subpopulation exhibited the majority of the inhibitory effect.
Conclusions:
- iIEL possess a significant inhibitory action on lymphocyte proliferation.
- The inhibitory function is mediated by lymphoid cells, specifically the CD8+ population.
- The CD8αα+ iIEL subpopulation is primarily responsible for suppressing immune responses in this model.
Unlabelled:
The intestinal intraepithelial lymphocytes (iIEL) may play a critical role in preventing overwhelming sensitization to foreign luminal antigens. The purpose of this experiment was to identify the subpopulation of the iIEL responsible for this inhibitory action. One-way mixed lymphocyte cultures (MLC) were performed with rat splenocytes [Brown Norway (BN) as responder; irradiated Lewis as stimulator]. BN iIEL (comprising 5% of cells per well) were added to assess inhibitory function. In the control group, irradiated BN splenocytes were added to maintain identical cell numbers. Proliferation assays were expressed as mean counts per minute (CPM) +/- SD. Subpopulations of the iIEL were created by biomagnetically extracting iIELs labeled with monoclonal antibodies. The addition of iIELs to the MLC resulted in a 59% reduction in proliferation (P < 0.05). When the CD45+ population was removed from the iIEL this inhibitory activity was lost. Removal of the CD8+ population, but not the CD4+ population, also caused a loss of inhibitory activity. Separate analysis of either CD8(alpha)(alpha)+ or CD8(alpha)(beta)+ subpopulations identified the CD8(alpha)(alpha)+ population as having the majority of the inhibitory effect.
In Conclusion:
1) The iIEL has an inhibitory action on proliferation. 2) The involved population is of lymphoid origin, as a loss of CD45+ cells resulted in a loss of inhibition. 3) Loss of CD8+ iIEL cells resulted in a loss of inhibition demonstrating that these cells are responsible for this action. This inhibitory activity appears to be restricted to the CD8(alpha)(alpha)+ subpopulation.
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