Adenosine deaminase (ADA) is involved in purine metabolism and plays a significant role in the mechanisms of the immune system. The aim of this study was to investigate the activity of total ADA (tADA) and its isoenzymes ADA1 and ADA2 in serum and peripheral blood lymphocytes (PBLs) of children with juvenile rheumatoid arthritis (JRA) and systemic lupus erythematosus (SLE) in different phases of the diseases. The study comprised 34 patients with rheumatic disease, 24 with JRA and 10 with SLE, and 64 healthy controls. The tADA activity and its isoenzymes were measured in serum and PBLs of all patients by the method of Giusti and by the presence or absence of EHNA (erythro-9-(2-hydroxy-3-nonyl)adenine) during the active phase of the disease (before treatment), as well as during remission and relapse. Our data show that increased tADA activity in the serum and PBLs of patients with JRA and SLE is correlated mainly to increased levels of ADA2 activity in serum and ADA1 activity in PBLs. It also closely correlates with clinical disease activity and relapse. The cause of this increased tADA/ADA2 activity in serum and tADA/ADA1 activity in PBLs in JRA and SLE remains to be elucidated. Nevertheless, it may be noted that the measurement of tADA activity, together with ADA2 activity in serum and tADA with ADA1 activity in PBLs, could offer a biochemical approach to the assessment of the pathophysiology of JRA and SLE. Also, tADA and its isoenzymes could be used as alternative parameters representing disease activity.

A prospective study was undertaken to assess the usefulness of leukocyte count, serum C-reactive protein (CRP), procalcitonin (PCT), and the activities of total adenosine deaminase (tADA) and its isoenzymes ADA1 and ADA2, in the aetiological diagnosis of pneumonia in children. The study included three groups. Group A consisted of 23 children with bacterial pneumonia, group B of 50 children with viral and mycoplasmal pneumonia and group C of 46 healthy children. On the first day of admission in the clinic, blood samples were collected before the start of antimicrobial treatment, for culture, serological tests, leukocyte count and for the determination of CRP and PCT levels as well as tADA activity and its isoenzymes ADA1 and ADA2. According to our results, the mean leukocyte count and the mean concentrations of PCT and CRP were significantly higher in the children of group A than those in groups B and C. The admission serum PCT concentration has a higher sensitivity, specificity and positive predictive value for bacterial pneumonia than either CRP or the leukocyte count. The mean serum tADA, ADA1 and ADA2 activity in children of group A was not significantly different from those in group C, while the difference between groups B and C was statistically significant. In conclusion, we found that CRP is a good marker for screening various infectious diseases, but it cannot be used to distinguish between bacterial and viral infections. Serum PCT measurement might be a useful tool for the physician for the aetiological diagnosis of pneumonia in children. Measurements of serum tADA and ADA2 activity may provide useful additional diagnostic information on the aetiology of pneumonia so that appropriate antibiotic therapy can be given promptly. Further studies with larger patients groups are required to confirm our results.

Normal pregnancy is characterized by suppressed cell-mediated immunity. Adenosine deaminase (ADA) is a purine metabolic enzyme enriched in trophoblast cells of the placenta. It is an early marker of trophoblast cell differentiation. Also, the activation of ADA gene expression in the placenta is crucial and essential for proper fetal development. The activity of ADA shows changes in diseases characterized by the alteration of cell-mediated immunity. The purpose of this study was to assess the possible role of the alteration of cell-mediated immunity in women with recurrent spontaneous abortions (RSA) as a cause of changes in tADA activity, and also to evaluate the extent of the contribution of ADA1 and ADA2 to changes of tADA activity in serum and peripheral blood lymphocytes (PBLs). We measured in serum and in PBLs activities of tADA, ADA1 and ADA2 of 25 married women with RSA (group A) and of 28 healthy non-pregnant women (group B). According to our results in women with RSA, mean serum tADA, ADA1 and ADA2 activities were significantly higher than those of non-pregnant women (p < 0.001, p < 0.05 and p < 0.05 respectively). In women with RSA, mean PBLs tADA, ADA1 and ADA2 activities were significantly higher than those of non-pregnant women (p < 0.001, p < 0.05 and p < 0.05 respectively). The findings of this study show a marked increase of serum and PBLs ADA activities, which is derived from an increase of ADA2 and ADA1 activity in women with RSA. These changes reflect cell-mediated immunological changes.

Infections caused by the nematode Trichinella spiralis (T. spiralis) are characterized by an inflammatory response in the host. The aim of this study was to identify and evaluate markers for monitoring mice infected with T. spiralis and treated with or without mimosine. The markers that have been used were total and differential white blood cell counts, subpopulations of lymphocytes, serum tADA and its isoenzymes ADA1 and ADA2 activity. The study included 3 groups of BALB/c mice. Group A consisted of 16 healthy mice, Group B of 16 mice infected with T. spiralis and treated with saline, and Group C of 16 mice infected with T. spiralis and treated with mimosine. The measurements were made once per week for the first six weeks continuously following the infection. According to our results, leukocytosis, lymphocytosis and increased percentages of adhesion molecules and CD4 lymphocytes were present in groups B and C one week post-infection. Total ADA activity as well as ADA1 and ADA2 was higher in groups B and C versus group A from the first week post-infection. The levels of tADA activity, ADA1 and ADA2 were higher in group B compared to those of group C and the difference was statistically significant (p<0.05) during the 4th week post-infection. The majority of tADA activity, essential for an efficient immune response, was derived from ADA1 which may have been produced by infected tissues. The elevated activities of tADA and ADA1 may be sensitive markers for infection of T. spiralis and for monitoring the course of the infection.

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