citation needed. This meta study seems to not have found many biological links: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1361287/
Brief naturalistic stressors (such as exams) tended to suppress cellular immunity while preserving humoral immunity. Chronic stressors were associated with suppression of both cellular and humoral measures
The more a stressor deviated from those parameters by becoming more chronic, however, the more components of the immune system were affected in a potentially detrimental way.