Serum and Pleural Adenosine Deaminase Activity: Correct Interpretation of the Findings

Abstract

To the Editor: The assay of adenosine deaminase (ADA) activity in the serum and other biologic fluids is very useful for an accurate diagnosis of many pathologic conditions. For many years, we have routinely tested ADA activity in samples of biologic fluids of both inpatients and patients from other clinics. In 1973 we were the first to report that this enzymatic activity was constantly high in the cerebrospinal fluid (CSF) of subjects with tuberculous meningitis,1Piras MA Gakis C Cerebrospinal fluid adenosine deaminase activity in tuberculous meningitis.Enzyme. 1973; 14: 311-317Google Scholar and in 1978 we found a high activity of the same enzyme in pleural effusions of tubercular origin.2Piras MA Gakis C Budroni M Andreoni G Adenosine deaminase activity in pleural effusions: an aid to differential diagnosis.Br Med J. 1978; 2: 1751-1752Crossref PubMed Scopus (169) Google Scholar Moreover, we also found high ADA activity in pericardiac and articular effusions and in the few samples (five) of ascitic fluid that originated from tubercular disease. As for the ADA activity in the serum, we have observed its increase in many infectious diseases caused by microorganisms infecting mainly the macrophages, in human immunodeficiency virus (HIV) infection,3Gakis C Calia G Naitana A Pirino D Serro G Serum adenosine deaminase activity in HIV positive subjects: a hypothesis on the significance of ADA-2.Panminerva Med. 1989; 31: 107-113PubMed Google Scholar and in some malignant conditions.4Gakis C Piras MA Romani G Unusual biochemical pattern of serum adenosine deaminase activity in acute lymphoblastic leukemia.Haematologica. 1982; 67: 199-206PubMed Google Scholar In several papers on this enzyme, including the one by Fontes Baganha et al,5Fontes Baganha M Pêgo A Lima MA Gaspar EY Robalo Cordeiro A Serum and pleural adenosine deaminase: correlation with lymphocytic populations.Chest. 1990; 97: 605-610Abstract Full Text Full Text PDF PubMed Scopus (134) Google Scholar the description of the activity of ADA enzyme is surprisingly incomplete. This inaccuracy has prompted the writing of this communication, because the inaccuracy in fact leads to misinterpretation of some results, and in our view does not explain the reasons for its high activity. For a correct interpretation, we must take into account what is currently known about ADA activity5Fontes Baganha M Pêgo A Lima MA Gaspar EY Robalo Cordeiro A Serum and pleural adenosine deaminase: correlation with lymphocytic populations.Chest. 1990; 97: 605-610Abstract Full Text Full Text PDF PubMed Scopus (134) Google Scholar: (1) The ADA activity originates from the action of two principal isoenzymes, ADA-1 and ADA-2, which have different pH, Michaelis constant (Km), and relative substrate specificity patterns. (2) Adenosine deaminase 1 has low Km, optimal pH of 7.0 to 7.5, and a similar affinity for both adenosine and 2'-deoxyadenosine (2'-deoxyadenosine-ADA ratio of approximately 0.75). It is present in all tissues and is essential for an efficient immune response. The congenital absence of ADA-1 in the lymphocytes and erythrocytes causes severe combined immunodeficiency syndrome. (3) Adenosine deaminase 2 has a very high Km, an optimal pH of 6.5, a poor affinity for 2'-deoxyadenosine (2'-deoxyadenosine-ADA ratio of approximately 0.25),7Giusti G Galas C Temperature conversion factor, activation energy, relative substrate specificity and optimum pH of adenosine deaminase from human serum and tissue.Enzyme. 1971; 12: 417-425PubMed Google Scholar and is not related to severe combined immunodeficiency syndrome. It is found only in the monocyte macrophages5Fontes Baganha M Pêgo A Lima MA Gaspar EY Robalo Cordeiro A Serum and pleural adenosine deaminase: correlation with lymphocytic populations.Chest. 1990; 97: 605-610Abstract Full Text Full Text PDF PubMed Scopus (134) Google Scholar and not in other cells and is released by these cells when they are stimulated by the presence of live microorganisms in their interior.3Gakis C Calia G Naitana A Pirino D Serro G Serum adenosine deaminase activity in HIV positive subjects: a hypothesis on the significance of ADA-2.Panminerva Med. 1989; 31: 107-113PubMed Google Scholar This explains why ADA-2 increases in biologic fluids in the course of infectious diseases characterized by microorganisms infecting the macrophages. Therefore, it is of the utmost importance to establish whether high ADA activity in biologic fluid is due mainly to the presence of the isoenzyme ADA-1 or to the presence of ADA-2. Routinely we use a simple procedure to make such a distinction. We incubate identical quantities of a sample in two test tubes, one containing 20 mmol of adenosine substrate and the other 20 mmol of 2'-deoxyadenosine substrate, both at a pH of 6.5. We measure the enzymatic activity in each tube and then we calculate the 2'-deoxyadenosine-ADA ratio. By considering the relative substrate specificities, we found that enzymatic activity is mainly due to the presence of ADA-2 when we have both high ADA activity and a ratio below 0.45, while it is due to ADA-1 when we have high ADA activity and a ratio higher than 0.45.3Gakis C Calia G Naitana A Pirino D Serro G Serum adenosine deaminase activity in HIV positive subjects: a hypothesis on the significance of ADA-2.Panminerva Med. 1989; 31: 107-113PubMed Google Scholar,4Gakis C Piras MA Romani G Unusual biochemical pattern of serum adenosine deaminase activity in acute lymphoblastic leukemia.Haematologica. 1982; 67: 199-206PubMed Google Scholar,7Giusti G Galas C Temperature conversion factor, activation energy, relative substrate specificity and optimum pH of adenosine deaminase from human serum and tissue.Enzyme. 1971; 12: 417-425PubMed Google Scholar,8Zuckerman SH Olson JM Douglas SD Adenosine deaminase activity during in vitro culture of human peripheral blood monocytes and pulmonary alveolar macrophages.Exp Cell Res. 1980; 129: 281-287Crossref PubMed Scopus (35) Google Scholar The threshold of 0.45, established by experience, is suitable to distinguish approximately which of the two isoenzymes prevails in a given sample. Consequently, the interpretation of the significance of ADA activity in accordance with the findings just mentioned can be summarized briefly as follows: (1) A low 2'-deoxyadenosine-ADA ratio coupled with an increase in ADA activity in effusions and/or CSF suggests that a tubercular infection is behind the altered activity. Also, more recently we have found high ADA activity with the same features in the CSF in cases of cryptococcal meningitis (currently a common disease in HIV-positive subjects) (unpublished data). (2) In the same fluids, a ratio higher than 0.45 coupled with high or moderate ADA activity is found in subjects who have empyemic effusions or systemic malignant pathologic changes.9Gakis C Piras MA Saba F Romani G Longinotti M Rapporto 2'deossiadenosina/adenosina deaminasi nei versamenti pleurici e peritoneali: significato diagnostico.Boll Soc Ital Biol Sper. 1981; 57: 1835-1841PubMed Google Scholar(3) An enzymatic profile similar to that just described is found in the serum of patients with tumors (lymphomas, leukemias).10Gakis C Piras MA Romani G Saba F Longinotti M Behaviour of serum 2'deoxyadenosine/adenosine deaminase ratio in infectious diseases and haemopoietic malignacies.Int Res Commun Syst J Med Sci. 1981; 9: 518-519Google Scholar (4) Low ADA activity in the serum excludes typhoid fever, brucellosis,11Gakis C Calia G Cherchi GB Andreoni G Serum adenosine deaminase activity in brucellosis.Int Res Commun Syst J Med Sci. 1983; 11: 481-482Google Scholarrickettsiosis, and other infectious diseases that are characterized by microorganisms infecting the macrophages. More recently, we have found high ADA activity in the serum of three patients with visceral leishmaniasis (kala azar) (unpublished data). (5) Generally speaking, high ADA activity coupled with a low 2'-deoxyadenosine-ADA ratio indicates the presence of live microorganisms inside the macrophages.3Gakis C Calia G Naitana A Pirino D Serro G Serum adenosine deaminase activity in HIV positive subjects: a hypothesis on the significance of ADA-2.Panminerva Med. 1989; 31: 107-113PubMed Google Scholar It is evident from the above that the knowledge that ADA activity may be related to two isoenzymes that have different pH, Km, and relative substrate specificity patterns is of the utmost importance in correctly interpreting the results of ADA activity in biologic fluids. Serum and Pleural Adenosine Deaminase Activity: Correct Interpretation of the FindingsCHESTVol. 99Issue 6PreviewTo the Editor: Full-Text PDF