CEACAM5 and bacterial infectious disease: We also propose a role for the constitutively expressed CEACAM6 as well as CEACAM1 and CEACAM5 in the phenomenon of increased host susceptibility to bacterial infection upon viral challenge in the human respiratory tract, as it occours for example in COPD patients, since either enhanced CEACAM1 expression induced by viruses or the COPD-associated changes in the function of the mucociliary clearance that will allow an easy access to CEACAMs on respiratory epithelia are likely to increase bacterial colonization.