Teacher immunity as a novel construct, acts as a defense against the demands placed on teachers and the distressing experiences faced which result in emotional burnout. The main aim of this study was to draw attention to this overlooked dimension of teacher motivation and professional identity through exploring the immunity levels of the student-teachers at teacher education universities in Iran. Accordingly, a mixed method study was designed to which 175 Iranian student-teachers (98 males and 77 females) majoring in Teaching English as a Foreign Language (TEFL) were randomly invited to this study. Language Teachers Immunity Questionnaire (LTIQ) was used to collect quantitative data on teachers' immunity levels and a semi-structured interview was conducted to collect the qualitative data. After conducting coding and content analyses using MAXQDA and running one-way ANOVA and independent samples t-test, both qualitative and quantitative data were analyzed. The results led to the identification of three immunity types, namely, negative (maladaptive), neutral and positive (productive) types. The results indicated that positive or productive immunity type was dominant among the student teachers. In addition the results of the study indicated that unlike gender, the years of education was a significant factor in terms of determining the immunity levels of the student teachers. Furthermore, the results of the study indicated that teacher immunity is a transient, dynamic and organic construct which fluctuates according to the reinforcement or deficiency of its comprising components such as efficacy and attitude, among others.