In vivo preactivated autoreactive Th cells in healthy individuals

The direct analysis of autoantigen-specific Th-cells has been hampered so far by the lack of appropiate methods to directly determine their frequency or functional capabilities. We have applied a set of new techniques to directly identificate and analyze autoantigen-specific T-cells in both affected and healthy people according to their effector functions (e.g. effector cytokine production) after provocation with antigen.

We have used these technologies to analyze Th-cells specific for SLE-associated autoantigens, in particular nucleosomes and the ribonucleoprotein La. Suprisingly, in vivo pre-activated autoantigen-specific Th-cells secreting IFNgamma and TNFalpha, could be detected not only in SLE-patients, but also in normal healthy persons, with frequencies ranging from 0.02% to 0.1%. Preactivation of these cells in vivo was confirmed by the fact that they expressed CD45RO but not CD45RA. Some of them had down-regulated expression of CD45RB and CD27. We also detected in healthy donors in vivo preactivated Th-cell specific for the self-antigen alphaB-Cristallin, a small heat shock protein. Up to 0.5% of peripheral Th cells specifically react with IFNgamma secretion upon short term stimulation, a hallmark of a recall response, i.e. in vivo preactivation.

The fact that in vivo pre-activated, autoantigen-specific Th-cells can be detected at comparable frequencies and with similar cytokine secretion patterns in blood of normal persons and patients suffering from a disease in which such Th cells are suspected to play a pivotal role, points to mechanisms other than central and peripheral tolerance that control the initiation of those autoimmune reactions.