Elderly persons have a high incidence of lethal infections by encapsulated bacteria. However, mechanisms involved in their poor defense and maintenance of immunological memory have been poorly understood. The present study characterized the population of B cells known as IgM memory B cell compartment and their response by pneumococcal vaccine in elderly people. CD27+ memory B cells, particularly IgD+IgM+CD27+ IgM memory B cells, had dramatically declined in the aged. Their Ig syntheses by B cells and the differentiation into plasma cells were diminished in vitro compared with those in adults. A rise of anti-pneumococcal IgM in sera of elderly persons was found with lower levels compared with those in adults after pneumococcal vaccination. Although diminished function itself of aged B cells surely exist, decline of the IgM memory B cell pool is expected to result in a poor humoral immunity against pneumococcal infection in elderly people.

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The Fc receptor common γ-chain (FcRγ) is a widely expressed adaptor bearing an immunoreceptor tyrosine-based activation motif (ITAM) that transduces activation signals from various immunoreceptors. We found here that basophils lacking FcRγ developed normally and proliferated efficiently in response to interleukin 3 (IL-3), but were severely impaired in IL-3-induced IL-4 production and in supporting T helper 2 cell differentiation. Through the transmembrane portion, FcRγ associated constitutively with the common β-chain of the IL-3 receptor and signaled via recruiting the kinase Syk. Retrovirus-mediated complementation revealed the essential role for the ITAM of FcRγ in IL-3 signal transduction. These results uncover a novel mechanism for FcRγ function to 'route' selective cytokine-triggered signals into the ITAM-mediated IL-4 production pathway.Hida et al.

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