Virus World

In our studies of human tissue immunity that used samples that were obtained from deceased human organ donors, we consistently observed that lymph nodes (LNs) associated with the lungs were black in color, owing to the presence of black particulate matter, whereas gut-associated LNs were the expected beige color, with no particulates. Thus, we began to investigate the effect of particulates on immune cells and LN architecture in these different LN sites using quantitative imaging and cellular and functional assays. We found that atmospheric particulate matter accumulated with age specifically in lung-associated LNs but not in gut-associated LNs, and this accumulation increased remarkably after age 40 (Fig. 1). Because lymphatic vessels connect LNs and tissues, one might expect that black particulates would disperse across other types of tissue-draining LNs; however, the fact that particulates became entrapped in lung-associated LNs suggested local effects of particulate matter on lung immunity. We found that particulates were contained within a specific subset of macrophages that was located in the T cell zone of the LN and not within follicles. Importantly, particulate-containing macrophages exhibited reduced activation, impaired production of pro-inflammatory cytokines and significantly reduced phagocytic capacity, whereas macrophages in the same LN that did not contain particulates did not exhibit these functional alterations. Particulate accumulation in lung-associated LNs further led to age-associated alterations in LN structural integrity, owing to the disruption of B cell follicles and lymphatic drainage. These results show that inhaled particulates have direct and cumulative effects on innate and adaptive immune processes that take place in the lymphoid organs that carry out immune surveillance of the lungs and respiratory tract.

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