From my understanding CD28 binds TCRs. However, if there are antigen-presenting MHCI cells also present in the culture media, would the CD28 compete with the antigen?
So if I want an antigen-specific CD8 response should I omit CD28 in the culture media?
Antigen loaded on to the MHC molecule on APC binds to TCR on the T cell surface and this is signal one. CD28 expressed on the T cell binds to CD80/CD86 expressed on antigen presenting cells and provides co-stimulation (signal 2). Hence, they are not competing for the same binding partners. Antigen specific T cell responses are usually determined by plating T cells with the cognate antigen (protein or peptides) and IL-2.
No worries. However, the same principle applies here. anti-CD3 binds to CD3 receptor on the T cell surface, not TCR. Therefore, there is no competition. I would still not use it in culture when looking for antigen specific responses. This is coz anti-CD3 could bind to CD3 and activate T cells independent of the antigen. If you have anti-CD3 in the culture, the responses you measure are not going to be antigen specific.
Meant to link this review but forgot.
Article The T-cell-receptor signaling network
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