cells use finger-like protrusions called ‘microvilli’ to interrogate their targets, but why they do so is unknown. T-cell contact with target cells is mediated by adhesive proteins acting alongside highly charged, barrier-like layers of large glycoproteins forming each cell’s glycocalyx. Here, T cells were observed to use microvilli to overcome the glycocalyx barrier, forming numerous, small (<0.5 μm diameter) contacts each of which was stabilized by the small adhesive protein CD2 and excluded large proteins including ICAM-1 and CD45, allowing sensitive, antigen-dependent TCR signaling. Importantly, in the absence of the glycocalyx or when we increased microvillar contact-size by enhancing CD2 expression, we observed strong signaling that was no longer antigen dependent. Our observations indicate that, modulated by the opposing effects of the glycocalyx and small adhesive 25 proteins, the use of microvilli equips T cells with the ability to effect discriminatory receptor signaling.