| Background and Objective Asthma is chronic airway immune inflammation characterized by airway lymphocyte infiltration and eosinophilia, airway hyperresponsiveness(AHR) and mucus hypersecretion. The prevalence of asthma has increased steadily worldwide over the past decades, which has become a major public health issue for the industrialized world. In China, it is severe that prevalence of asthma in children aged 0~14 years increased 1.6-fold from 0.78 % in 1990 to 2.06 % in 2000. "Hygiene hypothesis" suggests that the improved hygiene in industrialized countries and the use of vaccines and antibiotics has caused the decline of many infectious diseases that would normally stimulate the immune system in some way that mitigates against asthma. But the underlying mechanisms remain to be elucidated. According to "Hygiene hypothesis", BCG vaccination may protect from asthma. Multiple studies in animal models have demonstrated consistently that treatments with BCG are capable of inhibiting allergen-induced lung inflammatory responses. However, it is controversial whether BCG vaccination could decrease asthma prevalence in human. Almost every neonate receives BCG vaccination in mainland of China, but increase in asthmatic prevalence implies impropriety of viewpoint about BCG vaccination protecting from asthma in human. Furthermore, respiratory syncytial virus (RSV) is the leading viral respiratory pathogen in infants and young children worldwide and associated closely with development of childhood asthma. Here, we proposed a hypothesis that the anti-asthma role of BCG vaccination in human might be reversed by virus such as RSV infection. To test the hypothesis mentioned above and explore possible mechanisms, we conducted experiments adapting mouse model in three parts. Part one, to explore the effects of neonatal BCG vaccination on immune functional development of splenic T cells. Part two, to study the impact of neonatal BCG vaccination on lung inflammation and immune status after RSV infection. Part three, to investigate whether BCG-anti-asthma effect is reversed by RSV infection. Methods Part one. Neonatal clean BALB/c mice were inoculated with BCG by i.p. After 4 weeks later, spleen cells of mice were isolated and surface molecules CD4, CD25 and CD44 and intracellular IFN-γ, IL-10,and IL-4 in CD3+ T cells were detected by flow cytometry. Furthermore, mRNA expression of transcription factor T-bet, Foxp3 and GATA-3 were analyzed by RT-PCR. Part two. Neonatal BALB/c mice were divided into four groups, n=8 per group. Control was mock-vaccinated and mock-infected. BCG group was BCG-vaccinated and mock-infected. RSV group was mock-vaccinated and RSV-infected. BCG+RSV group was BCG-vaccinated and RSV-infected. Mice were vaccinated with BCG as newborns and infected with RSV at 3 weeks of age. Body weights of mice were measured daily for 7 days after RSV infection. Lung inflammation was assessed by bronchoalveolar lavage (BAL) and histopathology at 4 weeks. Cytokines ( IFNγ,IL-4 and IL-10) in BAL fluid (BALF) were detected by ELISA. Expression of TLR2 and TLR4 mRNA were analyzed by RT-PCR. Part three. Neonatal BALB/c mice were divided into five groups, n=8 per group. Control and OVA group were mock-vaccinated as newborns and mock-infected at 3 weeks of age. BCG/OVA group was BCG-vaccinated and mock-infected. RSV/OVA group was mock-vaccinated and RSV-infected. BCG/RSV/OVA group was BCG-vaccinated and RSV-infected. Except for control group, other groups undergone ovalbumin (OVA) sensitization and challenge. Bronchoalveolar lavage was performed and airway responsiveness to inhaled methacholine was measured after challenge. Cells in BALF were counted. Cytokines in BALF and serumOVA-specific IgE were detected by ELISA and inflammatory characteristics of lungs was scored by staining with hematoxylin and eosin. Results Part one. (1) Average weight of murine spleens from BCG group was significantly higher than that from control (P<0.05). (2)The percentage of total CD4+ T cells was less (P<0.01) with more percentag...
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