Adenosine deaminase activity in cats infected with feline immunodeficiency virus

Adenosine deaminase (ADA), an enzyme involved in purine metabolism, has been shown to be of clinical importance in several diseases in humans. To investigate whether ADA is of any clinical significance in cats, plasma adenosine deaminase (P-ADA) and T cell adenosine deaminase (T-ADA) activities were measured in feline immunodeficiency virus (FIV) negative and positive cats. The AIDS-related complex (ARC) group showed a significant elevation in P-ADA activity compared to the asymptomatic carrier (AC), and FIV-negative groups (P<0.005). T-ADA activity was significantly elevated in FIV-positive cats compared to the FIV-negative group (P<0.05) and this elevation was attributed to the increase in the ARC group (P<0.01). A correlation was found between P-ADA and T-ADA activities in the FIV-negative group. T-ADA activity and CD4(+)cell number showed a strong negative correlation in FIV-positive cats (P<0.0005). CD4(+) cell numbers were significantly reduced in the ARC group compared to the healthy controls (P<0.005). Our results showed that T-ADA is increased in FIV-positive cats during the ARC stage. These results also suggest that ADA may be an indicator of T cell activation in the ARC stage of FIV infection.