Pretreatment With Inactivated Bacillus Calmette–Guerin Increases CD4+CD25+ Regulatory T Cell Function and Decreases Functional and Structural Effects of Asthma Induction in a Rat Asthma Model

Bacillus Calmette-Guerin (BCG) has been shown to have therapeutic effects on asthma through CD4+CD25+ regulatory T cells (Tregs). We sought to assess pretreatment with inactivated BCG on CD4+CD25+ Tregs and its functional and structural effects in rat asthma model. The rat asthma model was established using ovalbumin (OVA) sensitization and challenge. Ten rats were pretreated with BCG prior to OVA and received continued BCG injections during OVA challenge (BCG+OVA group), 10 rats were treated with OVA alone (OVA group), and 10 rats were treated with saline (control group). After 9 weeks, histamine dihydrochloride effect on airway resistance was measured. Number of CD4+CD25+ Tregs was measured by flow cytometry, expression of Foxp3 and CTLA-4 mRNA was measured, and serum TGF-β levels were determined. Differential cell count in bronchoalveolar lavage fluid (BALF) was determined, and lung tissue was processed and stained with hematoxylin and eosin, Masson's trichrome, and alcine blue and periodic acid Schiff's reaction to evaluate inflammatory cell infiltration, collagen deposition, and presence of goblet cells, respectively. BCG treatment led to an increase in CD4+CD25+ Tregs, as well as an increase in Foxp3 and CTLA-4 expression and serum TGF-β levels. In addition, we observed a decrease in histamine dihydrochloride-induced airway resistance, a decrease in inflammatory leukocytes in BALF, and a decrease in airway remodeling indicators in BCG+OVA-treated rats compared with OVA-treated rats. Intradermally injected inactivated BCG has the potential to improve airway inflammation, airway resistance, and airway remodeling through a mechanism that may involve CD4+CD25+ Tregs.