Enhanced immune response to pneumococcal infection in malnourished mice nasally treated with heat killed Lactobacillus casei.

BARBIERI NATALIA; VILLENA JULIO; SALVA SUSANA; HERRERA MATÍAS; ALVAREZ SUSANA

San Miguel de Tucumán. Tucumán. Argentina

Simposio; III International Symposium on Lactic Acid Bacteria. II Argentinean LAB Net Meeting; 2009

CERELA-CONICET

This work analyzed whether the nasal administration of viable and non-viable Lactobacillus casei CRL 431 to immunocompromised mice was capable of increasing resistance against Streptococcus pneumoniae infection. Weaned mice were malnourished after consuming a protein-free diet (PFD) for 21 days. Malnourished mice were fed a balanced conventional diet (BD) for 7 days or BD for 7 days with viable or non-viable L. casei nasal treatments (109 cells/mouse/day) on days 6 and 7 (BD+LcV and BD+LcN, respectively). The malnourished control group (MNC) received PFD while the well-nourished control (WNC) mice consumed BD. In addition, malnourished mice replete only with BD were used as controls (BDC group). At the end of treatments the different groups of mice were infected nasally with S. pneumoniae (105 cells/mouse). The resistance against the pathogen and the innate and specific immune responses were studied during 10 days after the challenge. MNC mice showed greater lung colonization, more severe lung injuries, impaired leukocyte recruitment and reduced antibodies and cytokine production when compared with WNC mice. Administration of L. casei increased the resistance of malnourished mice to the infection. Both BD+LcV and BD+LcN treatments prevented the dissemination of the pathogen to the blood and induced its lung clearance (Lung bacterial cell count: WNC=3.2±0.12 log CFU/ g lung; MNC=5.91±0.11; BDC=4.4±0.11; BD+LcV<1.5; BD+LcN<1.5). BD+LcV and BD+LcN groups showed improved production of TNF-á and activity of phagocytes in the respiratory tract, an effect that was not observed in the BDC control group (Respiratory TNF-á: WNC=35.6±9.3 pg/mL; MNC=33.1±7.2; BDC=34.2±6.2; BD+LcV=48.9±7.9; BD+LcN=59.5±8.5). In addition, IL-4 and IL-10 were significantly increased in BD+LcV and BD+LcN groups, which correlated with the increase in the levels of specific respiratory IgA (Respiratory IgA: WNC=2.65±0.99 mg/L; MNC=1.38±1.18; BDC=1.48±1.15; BD+LcV=6.48±1.36; BD+LcN=5.57±0.91). The nasal treatments with L. casei were also effective to stimulate the production of specific IgG at both the systemic and the respiratory levels. (Serum IgG: WNC=27.97±1.81 mg/L; MNC=9.33±1.60; BDC=14.27±2.18; BD+LcV=42.3±2.67; BD+LcN=32.45±2.09). Results showed that nasal administration of L. casei is able to improve the innate and specific immune responses against S. pneumoniae in malnourished immunocompromised mice. The comparative study between the viable and the non viable bacteria demonstrated that viability would be an important factor to achieve maximum protective effect. However, the results from this study suggest that heat-killed lactic acid bacteria are also effective in the immunomodulation of the systemic and respiratory immune system.