'autoimmunize' is built from the Greek prefix 'auto-' meaning 'self' and the element 'immunize,' ultimately from Latin 'immunis' meaning 'exempt' (via Medieval/Modern usage meaning 'protected from disease'); the verbal suffix '-ize' (from Greek/Latin/French formation) turns it into an action word. 'autoimmunizing' is the present-participle/adj. form of that verb.

'autoimmunize' is a modern compound formed in English in the 20th century from 'auto-' + 'immunize' (itself from Latin 'immunis' through Medieval/Modern use of 'immune' and the verb-forming suffix). The compound arose as medical understanding of autoimmune phenomena developed; it did not evolve through distinct Middle English stages but was formed productively in modern scientific English.

Originally components meant 'self' (auto-) and 'exempt/protected' (immunis); combined in modern medical usage they came to mean provoking or developing an immune response directed at the self — a technical sense tied to immunology.