Monocytes control gamma/delta T-cell responses by a secreted product

Area of Science:

• Immunology
• Cell Biology

Background:

• Bovine monocytes play a role in immune regulation.
• Gamma/delta T cells are involved in specific immune responses.

Purpose of the Study:

• To investigate the mechanism by which ex vivo bovine monocytes regulate gamma/delta T-cell proliferation.
• To determine if this regulation is specific to gamma/delta T cells.

Main Methods:

• Autologous mixed lymphocyte reaction (AMLR) assays with gamma-irradiated and non-irradiated bovine monocytes.
• Transwell assays and supernatant transfer to assess soluble factors.
• Testing effects of IL-2, anti-WC1 antibodies, nitric oxide, ROS, PGE2, and TGF-beta.
• Assessing inhibition sensitivity to heat and monocyte activation states.

Main Results:

• Non-irradiated monocytes inhibited gamma/delta T-cell proliferation in AMLR, while irradiated monocytes induced it.
• Inhibition was specific to gamma/delta T cells and not due to cell death or generalized unresponsiveness.
• The inhibitory effect was mediated by a soluble product secreted by monocytes within the first 6 hours of culture.
• The inhibitory factor was heat-sensitive (at 65°C) but not nitric oxide, ROS, PGE2, or TGF-beta.
• Monocyte activation by LPS or GM-CSF temporarily abolished inhibition, while heat-shocking did not.

Conclusions:

• Bovine monocytes produce a soluble, heat-sensitive inhibitor of gamma/delta T-cell proliferation.
• This inhibition is specific to gamma/delta T cells and is regulated by the monocyte's activation state.
• The findings suggest a physiological role for monocytes in controlling gamma/delta T-cell responses in vivo, which can be disrupted by monocyte alteration.