Abstract: AIM To further identify the response of brain areas to the immune stimulus. METHODS Using immunohistochemistry method, we observed the Fos expression in the brain of purified protein derivative of tuberculin (PPD) immunized mice at different time points. RESULTS At 3, 9, 14, 18, 21 d following the primary immunization and 7, 14 d following the second immunization, strong Fos immunostaining was observed in many brain areas such as the ventrolater-al medulla, central gray, hippocampus and neocortex. But the patterns at different time were not completely the same, especially in the cingulate cortex. Fos expression in the right side is stronger than that in the left side after second immunization with PPD. CONCLUSION It is suggested that many brain areas participate in the interaction of immune and central nervous system, and that brain asymmetry might be associated with the peripheral immune response.