Detection of tetanus toxoid-specific memory T cells in equine lymph nodes but not in peripheral blood.

This research article explores the use of tetanus toxoid for testing equine immune responses. It found that horse lymph node cells responded to the toxoid, but peripheral blood cells did not; this was due to a lack of antigen recognition, rather than the presence of a suppressive factor.

Investigation of the Use of Tetanus Toxoid

• The researchers were interested in using tetanus toxoid (an inactive form of tetanus toxin used in vaccines), as a ‘recall antigen’. This is an antigen that the immune system has encountered before and should ‘remember’, producing a more rapid secondary immune response.
• Theoretically, tetanus toxoid could provide a useful and cost-effective way to test immune responses in horses if their immune cells respond to it in laboratory conditions.

Testing the Response of Immune Cells to Tetanus Toxoid

• Peripheral blood mononuclear cells (PBMCs) and lymph node mononuclear cells were collected from horses that had previously been immunised with tetanus toxoid.
• The researchers attempted to stimulate these cells with tetanus toxoid and then measured their proliferative response – the increase in cell number due to cell growth and division that indicates an active immune response.

Results: No Proliferative Response in PBMCs

• No proliferative response to tetanus toxoid was observed in the horse PBMCs, regardless of how the cells were cultured.
• However, lymph node mononuclear cells from the same animals did show significant proliferation in response to the tetanus toxoid.

Investigating the Reasons for Lack of Response

• The researchers established that the lack of response from PBMCs was not due to a suppressive factor inhibiting their proliferation.
• Instead, they concluded that the T cells within the PBMCs were simply not recognising the tetanus toxoid as an antigen.

Implications of the Study

• This result has implications for the use of tetanus toxoid as a recall antigen in equine immune studies. As ideally, a recall antigen should stimulate an immune response in all cells with a memory of that antigen.
• The failure of the PBMCs to respond suggests that they may not be a reliable cell type to use for these types of tests.