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By Kirsty Oswald, medwireNews Reporter

Research shows that smoking status, and not airway obstruction, determines the distribution of T cell subsets in bronchoalveolar lavage (BAL) in patients with chronic obstructive pulmonary disease (COPD).

The researchers, led by Helena Forsslund (Karolinska Institute, Stockholm, Sweden), say that the findings underline the importance of considering non-smoking patients with COPD as a separate subgroup.

“We conclude that current smoking status is crucial when the inflammatory response in COPD is evaluated,” they write in Chest.

“We would therefore like to stress the importance of subtyping COPD patients, in particular with regards to smoking habits.”

The team studied 27 current smokers and 11 ex-smokers with COPD at Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage I or II, and compared them with 40 never-smokers and 40 smokers with normal lung function.

The percentage of CD8+ T cells – which are thought to play a key role in the pathogenesis of COPD – was significantly higher in BAL fluid from smokers with and without COPD compared with that from never-smokers without COPD. And, COPD ex-smokers had a significantly lower percentage of CD8+ cells than both smoking groups. The proportion of CD4+ T cells – which by contrast are thought to play a role in emphysema at the more severe end of the disease – was significantly reduced in both smoking groups relative to both never-smokers without COPD and ex-smokers with COPD.

Accordingly, the ratio of CD4+ to CD8+ count was significantly lower in both smoking groups than never-smokers and ex-smokers with COPD.

Additionally, both groups of smokers had a significantly higher proportion of natural killer T-like cells in BAL compared with never-smokers and COPD ex-smokers, and as among T-cells, the proportion of CD8+ was significantly increased and that of CD4+ significantly reduced.

The team notes that in peripheral blood these trends were typically reversed, indicating preferential recruitment of CD8+ cells to the lung.

The researchers also found that the percentage of CD8+ T cells in BAL liquid was significantly and positively associated with the number of cigarettes smoked per day in the past 6 months, a relationship that was particularly strong among men.

By contrast, there was no association between lymphocytic subpopulations in BAL and any patient characteristics, including markers of systemic inflammation, gender, GOLD stage, and the presence or absence of chronic bronchitis.

“Current smoking status has a greater impact than airway obstruction on the distribution of T cell subsets in BAL of patients with mild to moderate COPD,” write Forsslund and colleagues.

“This must be considered when the role of T cells in COPD is evaluated,” they conclude.

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