Decreased expression of Th2 type cytokine mRNA contributes to the lack of allergic bronchial inflammation in aged rats

Sensitized Brown Norway rats are known to develop eosinophilic bronchial in flammation and airway hyperresponsiveness after Ag exposure, However, we ha ve previously observed that sensitized aged rats of the same strain failed to develop such allergic inflammation. In the present study, we investigate d age-associated changes of cytokine mRNA expression in bronchoalveolar lav age (BAL) cells. Both young (8- to 10-wk-old) and aged (100- to 120-wk-old) Brown Norway rats were sensitized with OVA, and BAL was performed 24 h aft er OVA inhalation challenge. Semiquantitative RT-PCR analysis of BAL cells showed that the cells from aged rats preferentially expressed Th1 type cyto kine (IFN-gamma) mRNA, whereas cells from young animals expressed more Th2 type cytokine mRNAs including those for IL-4 and IL-5, Decreased expression of Th2 type cytokine transcripts in aged animals was further confirmed by quantitative analysis, competitive RT-PCR of BAL cells, and in situ hybridi zation, The age-associated changes of cytokine profile mere not restricted to BAL cells but were a general feature of lymphocytes, as shown by examina tion of popliteal lymph nodes draining the site of sensitization. These fin dings suggest that decreased allergic inflammation in aged animals is attri butable to age-dependent impairment of Th2 generation in response to Ag.