Nasal administration of a non-viable Lactobacillus casei to infant mice modulates lung damage induced by Poly I:C and hyperreactivity in airways.

Viral respiratory infections caused by RNA viruses are one of the most important diseases around the world. The aim of this work was to study whether the nasal administration of non-viable Lactobacillus casei (LcM) was able to enhance respiratory antiviral defenses in young mice challenged with Poly I:C. Three-week-old BALB/c mice were nasally challenged with Poly I:C, used to mimic the pro-inflammatory state of lung infections caused by RNA viruses. LcM was nasally administered 2 days before Poly I:C challenge. Lactate dehydrogenase (LDH) activity, albumin concentration in broncho-alveolar lavages (BAL), wet-to-dry lung weight ratio, and total and differential leukocytes counts in blood were evaluated. Also, α, λ, γ interferons, IL-10, TNF-α, IL-4 in BAL and nasal lavages and total IgE in BAL and serum, were evaluated by ELISA. Poly I:C induced pulmonary injuries while alteration of bronchoalveolar-capillary barrier was reduced by nasal administration of LcM. Moreover, alterations in leukocyte counts induced by Poly I:C were regulated. LcM favorably modulated the cytokines responses triggered by Poly I:C challenge in nasal and lung mucosal compartments. Also, LcM decreased IgE levels in BAL and plasma compared with the Poly I:C group. LcM nasally administered reduced the lung damage induced by Poly I:C and prevented airway hyperreactivity.