The present study explored the development of language teacher immunity among Iranian in-service English as a Foreign/Second Language (EFL) teachers (N=15) working at public high schools. Drawing on semi-structured interview data, the study found that low self-confidence, students' demotivation, low income, limited facilities, lack of enough time to teach English, parental expectations, and negative attitudes toward English were the main triggers of language teacher immunity among the participants. Reflecting on those disturbances, the participants employed certain coping strategies such as prior preparation, establishing a good rapport with learners, and exercising agency in providing required facilities and negotiating objectives with learners' parents. The strategies adopted by the participants revealed that reflective practice should be an integrated undertaking involving reflection on personal, sociocultural, and educational factors rather than being limited to practice per se. The study introduced "imposed maladaptive immunity" as a transitional stage from exercising agency to setting into a state of complete indifference due to lack of support from macro-level educational policy makers. Finally, the study implied that language teacher education programs should raise EFL teachers' awareness of the developmental stages of language teacher immunity as an integrated reflective practice.