Dept Biology, Center for Infectious Disease Dynamics, The Pennsylvania State University, University Park, PA 16802, USA.
BMC Microbiol. 2010 Aug 25;10:226. doi: 10.1186/1471-2180-10-226.
The role of host immunity has been recognized as not only playing a fundamental role in the interaction between the host and pathogen but also in influencing host infectiousness and the ability to shed pathogens. Despite the interest in this area of study, and the development of theoretical work on the immuno-epidemiology of infections, little is known about the immunological processes that influence pathogen shedding patterns.
We used the respiratory bacterium Bordetella bronchiseptica and its common natural host, the rabbit, to examine the intensity and duration of oro-nasal bacteria shedding in relation to changes in the level of serum antibodies, blood cells, cytokine expression and number of bacteria colonies in the respiratory tract. Findings show that infected rabbits shed B. bronchiseptica by contact up to 4.5 months post infection. Shedding was positively affected by number of bacteria in the nasal cavity (CFU/g) but negatively influenced by serum IgG, which also contributed to the initial reduction of bacteria in the nasal cavity. Three main patterns of shedding were identified: i- bacteria were shed intermittently (46% of individuals), ii- bacteria shedding fell with the progression of the infection (31%) and iii- individuals never shed bacteria despite being infected (23%). Differences in the initial number of bacteria shed between the first two groups were associated with differences in the level of serum antibodies and white blood cells. These results suggest that the immunological conditions at the early stage of the infection may play a role in modulating the long term dynamics of B. bronchiseptica shedding.
We propose that IgG influences the threshold of bacteria in the oro-nasal cavity which then affects the intensity and duration of individual shedding. In addition, we suggest that a threshold level of infection is required for shedding, below this value individuals never shed bacteria despite being infected. The mechanisms regulating these interactions are still obscure and more studies are needed to understand the persistence of bacteria in the upper respiratory tract and the processes controlling the intensity and duration of shedding.
宿主免疫在宿主与病原体的相互作用中不仅起着至关重要的作用，而且还影响宿主的传染性和病原体脱落能力。尽管人们对这一研究领域很感兴趣，并且对传染病的免疫流行病学理论也有了一定的研究，但对于影响病原体脱落模式的免疫过程却知之甚少。
我们使用呼吸道细菌博德特氏菌及其常见的天然宿主兔，研究了血清抗体、血细胞、细胞因子表达和呼吸道细菌菌落数量变化与口鼻细菌脱落强度和持续时间的关系。结果表明，感染后的兔子在接触后可通过口鼻排出博德特氏菌长达 4.5 个月。鼻腔中的细菌数量（CFU/g）会正向影响脱落程度，但血清 IgG 会负向影响脱落程度，同时也会导致鼻腔中的细菌数量最初减少。确定了三种主要的脱落模式：i-细菌间歇性脱落（46%的个体），ii-随着感染的进展，脱落逐渐减少（31%），iii-尽管感染了，但个体从未排出过细菌（23%）。前两组个体最初排出的细菌数量存在差异，这与血清抗体和白细胞水平的差异有关。这些结果表明，感染早期的免疫状况可能在调节博德特氏菌脱落的长期动力学方面发挥作用。
我们提出 IgG 影响了口鼻腔中的细菌阈值，从而影响了个体脱落的强度和持续时间。此外，我们还认为，需要达到一定的感染阈值才能发生脱落，否则个体即使感染了也不会排出细菌。调节这些相互作用的机制仍不清楚，需要更多的研究来理解上呼吸道中细菌的持续存在以及控制脱落强度和持续时间的过程。
