Bronchoalveolar lavage for the diagnosis of Pulmonary Langerhans cell histiocytosis.

BACKGROUND: The histologic diagnosis of Pulmonary Langerhans cell histiocytosis (PLCH) is invasive and can cause complications. To confirm the diagnosis of PLCH, guidelines therefore recommend measuring CD1a-positive bronchoalveolar lavage fluid (BALF) cells despite its poor sensitivity and specificity. Thus, an improved diagnostic accuracy of BALF cell analysis would be desirable.

METHODS: Using four-colour flow cytometry, plasmacytoid and myeloid dendritic cells (DCs) were analysed in BALF of 10 newly diagnosed, untreated, smoking patients with PLCH, and compared with BALF DCs from 40 asymptomatic smokers and 21 never-smokers.

RESULTS: Compared with controls, myeloid DCs (median: 0.79% of BALF leukocytes) and their subpopulation of Langerhans cells (median: 0.44% of BALF leukocytes) were not increased in PLCH. Patients with PLCH displayed a normal expression of the maturity marker CD83 on BALF myeloid DCs. However, the expression of the co-signaling molecule CD80 on BALF myeloid DCs was significantly lower than in both control groups, with the lowest expression found in more severe disease (presence of cysts > 2 cm in diameter). Based on receiver operating characteristic (ROC) curve analysis, a cut-off of 53% CD80-positive BALF myeloid DCs was optimal for the diagnosis of PLCH, yielding a sensitivity of 0.90 and a specificity of 0.90.

CONCLUSIONS: BALF Langerhans cells are not increased in PLCH. However, PLCH is characterised by a low expression of CD80 on BALF myeloid DCs. Due to its considerably higher sensitivity and specificity, this marker appears to be more appropriate to diagnose PLCH than the currently recommended marker CD1a.