IgG Subclasses in Bronchoalveolar Lavage Fluid from Patients with Asthma

We have measured Immunoglobulin G (IgG) subclasses in serum and bronchoalveolar lavage fluid (BALF) from 12 non‐smoking patients with stable asthma and 9 non‐smoking healthy volunteers to obtain information on their possible role in local immunological reactions. The quotients (concentration of IgG subclass in BALF)/(concentration of IgG subclass in serum) were calculated. In controls QIgG3 were lower than QIgGI, QIgG2 and QlgG4. The IgG subclasses in BALF and epithelial lining fluid (ELF) from patients with asthma were significantly higher than in controls, mainly due to increased leakage from the blood. Again QIgG3 were lower than Q of other subclasses. In the analysis of local production of IgG, albumin or ceruloplasmin was used as reference protein. Several patients showed a local production or a preferential accumulation of one or more IgG subclasses. We conclude that in healthy persons the IgG subclasses in ELF originate from the systemic circulation by passive permeation. In patients with asthma, the permeability of the respiratory membrane may be increased resulting in increased concentrations of subclasses in lung‐lining fluid. In some patients with asthma, an additional local production of IgG subclasses occurs.