Autoimmunity

Self-reactive lymphocytes are generated constantly and are normally removed or restrained. Central tolerance deletes them in the thymus and bone marrow, helped by AIRE-driven expression of tissue-restricted proteins so thymocytes meet antigens they would otherwise never see; peripheral tolerance handles escapees through regulatory T cells, anergy and deletion. Autoimmunity follows when those layers fail, through molecular mimicry between a microbial and a self epitope, release of sequestered antigen, epitope spreading, or HLA alleles that present a particular self peptide efficiently.

Autoimmune conditions affect several percent of the population, with marked female predominance. The serology is less decisive than it looks: a positive antinuclear antibody at low titre occurs in a substantial minority of healthy people, so the test has poor specificity alone, while anti-CCP antibodies are highly specific for rheumatoid arthritis and can precede symptoms by years. Checkpoint inhibitors prove the brakes are real, since removing them produces immune-related colitis, hepatitis, thyroiditis and hypophysitis in a large fraction of patients.

A positive autoantibody in a patient with low pretest probability is therefore more likely a false positive than a diagnosis, which is why panels ordered without a clinical question cause harm.

The claim to examine sceptically is that a peptide rebalances immunity with no autoimmune risk. Anything that genuinely increases T-cell activity carries risk of the same kind as checkpoint blockade, whatever its magnitude, and immunomodulators push in unexpected directions, as with the drug-induced lupus occasionally seen with anti-TNF agents. In the other direction, blaming a flare on a compound without temporal plausibility, dechallenge or any structured causality assessment is anecdote.