Why commonplace encounters turn to fatal attraction.

Focuses on the relationship between X-linked lymphoproliferative (XLP) disease with a specific virus that so vehemently elicits a disease phenotype. Finding that mutations to the SH2D1A gene predisposes to the fatal condition of XLP; Paradox of XLP in that the juxtaposition of a florid reaction to infection with the failure to establish an effective immune response.