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Concanavalin A-induced suppressor cell activity in intestinal mucosal leukocytes obtained from healthy cows
1Department of Veterinary Microbiology, University of Saskatchewan, Canada.
Insights
Bovine leukocytes activated by concanavalin A (conA) suppress immune responses. Monocytes/macrophages are crucial for this suppressor activity, which can be modulated by interleukin-2.
Area of Science:
- Immunology
- Gastrointestinal immunology
Background:
- The bovine small intestine harbors distinct leukocyte populations within the intraepithelium, lamina propria, and aggregated lymphoid follicles (ALF).
- Understanding the immunomodulatory functions of these leukocytes is crucial for gastrointestinal health and disease research.
Purpose of the Study:
- To investigate the inducible suppressor activity of bovine intestinal leukocytes activated by concanavalin A (conA).
- To elucidate the role of monocytes/macrophages and interleukin-2 in modulating these suppressor functions.
Main Methods:
- Isolation of leukocytes from different compartments of the bovine small intestinal mucosa.
- Activation of leukocytes with conA and assessment of suppressor activity against mitogen-stimulated autologous and allogeneic leukocytes.
- Depletion and reconstitution experiments using adherent cells (monocytes/macrophages).
- Evaluation of recombinant human interleukin-2's effect on responder cell proliferation.
Main Results:
- ConA-activated leukocytes from all three compartments exhibited suppressor activity against lymphocyte proliferation.
- Suppressor activity was dependent on the presence of adherent cells (monocytes/macrophages).
- Recombinant human interleukin-2 partially or fully restored proliferation in suppressed responder cells, with higher concentrations enhancing responses.
Conclusions:
- Bovine intestinal leukocytes, particularly those from ALF, possess inducible suppressor activity mediated by monocytes/macrophages.
- Interleukin-2 plays a significant role in regulating T-cell responses within the context of intestinal immunity.
- These findings contribute to understanding the complex immune regulation in the bovine gut.
Abstract:
Leukocytes isolated from the intraepithelium, lamina propria, and aggregated lymphoid follicles (ALF) of the bovine small intestinal mucosa were activated by concanavalin A (conA) to generate suppressor activity against the proliferative response of autologous and allogeneic leukocytes to conA, phytohemagglutinin, and pokeweed mitogen. Freshly obtained intraepithelium, lamina propria, and ALF leukocytes, preincubated with 25 to 50 micrograms/ml of conA for 24 to 48 hours, were able to inhibit the mitogenic responses of autologous and allogeneic lymphocytes when cocultured at a ratio greater than or equal to 1:1 (suppressor cells to responder cells). Depletion of adherent cells (monocytes/macrophages) by sequential plastic and gel adherence completely abrogated the conA-induced suppressor activity of all 3 leukocytes populations. However, reconstitution with autologous or allogeneic monocytes/macrophages during the induction phase restored the inducible suppressor activity. Addition of recombinant human interleukin-2 at a concentration as low as 5 U/ml during the responder phase enabled the responder population to recover the response apparently impaired by the conA-treated ALF leukocytes. At a concentration of 10 U/ml, human interleukin-2 was not only able to restore the responder population's response to phytohemagglutinin stimulation, but highly enhanced its proliferative ability. Although quantitative variations were observed between different cell populations and cells obtained from individual cows, the extent and general pattern of the inducible suppressor activity were similar in cells from cows studied.
