Quantitative Analysis of Influenza Virus-Specific B Cell Responses Generated by Infection and Vaccination

The two cellular components of B cell memory are antibody (Ab)-secreting cells (ASCs) and memory B cells (BMem). BMem are quiescent cells that respond to “recall” antigen and contribute substantially to vaccine effectiveness. The rational evaluation of vaccination strategies is dependent on quantitative information on the state of B cell memory. Despite the importance of BMem in resistance to infection, there is little information on the nature of BMem populations generated by influenza infection or vaccination. The major goal of this dissertation was a comprehensive quantitative analysis of the frequency and distribution of influenza-specific BMem generated by influenza infection of the respiratory tract, or by vaccination with inactivated virus. To achieve this, a prerequisite was the development of a sensitive and reproducible limiting dilution assay (LDA) for determining influenza-specific BMem frequencies. The results in Chapter 2 demonstrated that a strategy utilizing BPL-inactivated virus particles was effective for the in vitro activation of virus-specific BMem. This strategy selectively activates virus-specific BMem and, importantly, achieves this without a requirement for CD4+ T cell associated factors. Using this strategy, the frequency of Influenza specific BMem in different anatomical sites was measured and we also tested three different forms of influenza virus immunization strategy; (i) intranasal (i.n.) infection, (ii) i.n. vaccination, (iii) intramuscular (i.m.) vaccination. The results in Chapter III, IV showed that following different forms of immunization, BMem dispersed broadly to organized lymphoid tissues throughout the body, and a population of ASCs was established in the bone marrow. ASC and BMem frequencies in these locations reflected the magnitude of the primary B cell response to the form of immunization. Thus, the frequencies were higher following i.n. infection. Interestingly, the state of B cell memory in the lung was profoundly influenced by the form of immunization. The lung was a preferential site of BMem localization after i.n. infection. However, this was not the case after i.m. immunization when BMem frequencies in the lung were considerably lower than in other sites. Our findings point to an effect of influenza infection on the lung environment that profoundly influences ASC and BMem trafficking to this site