Significance of cerebrospinal fluid adenosine deaminase isoenzymes in tuberculous (TB) meningitis

Adenosine deaminase (ADA) exists as two isoenzymes, ADA(1) and ADA(2). It appears that the ADA(2) isoenzyme originates mainly from monocytes and macrophages. In tuberculous pleural effusions most of the ADA activity consists of ADA(2). The aim of this prospective study was to analyse ADA isoenzymes in the CSF of patients with meningitis to investigate whether the expected rise of the ADA(2) isoenzyme would occur in tuberculous meningitis. ADA isoenzyme analysis was performed on the CSF of 15 patients with tuberculous and 11 patients with bacterial meningitis by an automated kinetic enzyme coupled assay in the presence and absence of a specific ADA inhibitor. The ratio of ADA(2)/ADA(Total) was > 0.8 in 14/15 patients with tuberculous meningitis. In bacterial meningitis the ratio was > or =0.8 in 10/11 patients. The ADA(2) isoenzyme is the major contributor to increased ADA activity in the CSF of patients with tuberculous meningitis, probably reflecting the monocyte-macrophage origin of the ADA.