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Pneumococcal Pneumonia in the Elderly: The Eternal Question Is "Why?"

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The extremes of life represent periods of high health risks. We recognize that a number of factors create these 2 troublesome risk periods—developing or declining immune systems, close contact and crowding in daycare or eldercare, and critical organs that either haven’t reached their prime or have passed it. In their recent paper on pneumococcal pneumonia, Birjandi and Witte indicate, “Infection with pneumococcal pneumonia has been most successfully overcome in children, but it is still a problem in the elderly, particularly community-living older individuals.”

In this insightful summary, the authors indicate that the differences between the very young and the very old have been difficult to sequester. In both groups, the lungs have built-in ‘checkpoints’ to control pathogenic pneumococcal infection—checkpoint mechanism restrict colonization to upper airways, suppress invasive  strains, and can rapidly engage innate immune responses of alveolar epithelia, macrophages and neutrophils if necessary.

Why, then, are the elderly at greater risk than young children?

They propose that both groups have immunologic gaps against pathogenic bacteria, which trigger a subset of B lymphocytes called marginal zone (MZ) B cells located in the spleen. This response is T-cell-independent. In children, development of MZ B cells lags behind other immune cells, making them more susceptible to pnuemococal pneumonia.

In the senescent adult, less is known about MZ B cells. Elderly adults may be at increased riskfor pnuemococal pneumonia because of a premature demise in MZ B cells. They discuss a few known facts and possibilities:

They suggest future investigations should attempt to uncover reasons for MZM quantity decline, and determine if any intervention can replenish them.

Current vaccine therapies target T-independent responses to generate immunity against pneumococcus.