Is the measurement of virus-specific antibody in the lungs of transplant recipients with cytomegalovirus pneumonitis of diagnostic or prognostic value?

We have investigated 12 transplant recipients (nine bone marrow transplants, three renal) with 15 episodes of pneumonitis caused by cytomegalovirus (CMV) and ten patients (eight bone marrow transplant recipients, two renal transplant recipients) with 12 episodes of interstitial pneumonitis in whom no CMV was detected, to determine whether levels of CMV-specific IgG in the lung are diagnostic of infection. We have also assessed whether a vigorous specific local antibody response is important for survival. CMV-specific IgG and herpes simplex (HSV)-specific IgG were measured in bronchoalveolar lavage (BAL) fluid and serum using albumin to correct for simple diffusion from serum into the lung. We have found evidence for local production or facilitated transport of CMV-specific IgG in ten patients with CMV pneumonitis but also in six patients with pneumonitis where no CMV was detected. Similar results were found for HSV-specific IgG although only one patient had a demonstrable HSV infection. There was a tendency for those patients producing large amounts of immunoglobulin in the lung to survive compared with those who died, but there were wide variations between patients in each group. The local humoral immune response in transplant patients with pneumonitis was not specific to the infecting agent and is most probably the result of polyclonal B cell activation or facilitated transport of IgG from serum to lung secretions. Measurement of CMV-specific IgG response in the lung should not, therefore, be used for diagnostic or prognostic purposes.