NCAM1 and chronic obstructive pulmonary disease: In order to confirm whether this close physical interaction could be observed in COPD lung, double immunostaining of COPD lung sections for IL-18 and CD56 indicated that in lymphoid aggregates in the lung, IL-18-positive myeloid cells are indeed frequently in close proximity to CD56+ lymphoid cells, either NK cells or subsets of CD8+ T cells (Fig. 6d).