Diffusible signals enable communication between immune cells but can also create interference between nearby activation sites. In lymph nodes, effector T cells (Teff) concentrate around antigen-presenting cells (APCs), release interleukin-2 (IL-2) following antigen recognition, and sense IL-2 through cell-surface receptors. Experiments show high-uptake regulatory T cells (Treg) clustered around IL-2-producing cells. However, it is unclear how strongly responses at neighboring activation sites are coupled through diffusible IL-2, and how this coupling is influenced by the spatial organization of Treg acting as IL-2 sinks. We interpret two neighboring sites as a molecular communication system and study the effect of clustering using a three-dimensional IL-2 field coupled to T cell population dynamics. Across a broad parameter sweep, clustering Treg produces a larger mean reduction in neighboring-site interference than adding dispersed Treg. Compared with no Treg, clustered Treg suppress interference while largely preserving the strong local response with corresponding consequences for population expansion and survival. Information-theoretic analysis shows improved discrimination between weak and strong local sources at short separation, whereas at larger separation clustering primarily reduces the remaining estimated neighboring-source information. These findings support a spatial-filtering role for Treg clustering in maintaining locally informative immune responses.

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