Figure 1.

Butyrophilin 3 family member A1 (BTN3A1) is a pathogen-associated molecular pattern (PAMP) receptor. HMBPP from metabolically active bacteria, leaks into the cytoplasm where it is detected by the intracellular B30.2 domain of BTN3A1, triggering a conformational change within the protein. Thereby, the intracellular infection signal is transmitted through the plasma membrane to the surface, where BTN3A1 is constitutively associated with the Butyrophilin family member BTN2A1. Together they form an immunological synapse in which BTN2A1 interacts with the Vγ9 chain of the Vγ9Vδ2 TCR.