Frontiers in nephrology: heterologous immunity, T cell cross-reactivity, and alloreactivity.

Established memory T cell responses to a previously encountered pathogen can have a major impact on the course and outcome of a subsequent infection with an unrelated pathogen. This phenomenon, known as heterologous immunity, is dependent on the sequence of infections and can be either beneficial or detrimental to the host. Examples of heterologous immunity between unrelated viruses and alloantigens are mounting, and the role of cross-reactive T cells both in the pathogenesis of infections and in transplant rejection is now being explored. Memory T cells seem to be part of a continually evolving interactive network in which with each new infection, an alteration in the frequencies, distributions, and activities of memory cells is generated in response to previous infections and alloantigens.