A scaffolding model for antigen spreading. Shown is the target of an autoimmune response; here a snRNP particle that expresses at least two antigenic determinants. The determinant represented by the rectangle, which might be for example the PPPGRRP sequence on EBNA1, is assumed to cross react with the determinant PPPGMRPP on the snRNP via a conventional immune synapse. We denote progenitor B cells participating in these cognate interactions with T cells as primary progenitor B cells. Also shown is a second determinant on the small nuclear ribonucleoprotein particle (snRNP; represented by a circle) that is assumed to be more strongly disordered than the rectangular determinant. Progenitor B cells reacting with this determinant, termed secondary progenitor B cells, are capable of spreading the immune response via an eavesdropping mechanism as discussed in the text. EBV, Epstein-Barr virus.