481

after withdrawal of the drug, her liver function tests hadreturned to normal and a second liver biopsy showed repara-tive changes.

Departments of Internal Medicineand Rheumatology,

Ziekenhuis de Stadsmaten,Enschede, Netherlands

Department of Pathology,Streeklaboratorium voor Twente,en de Gelderse Achterhoek,

Enschede, Netherlands

R. TH. J. M. YPMAJ. J. M. FESTEN

C. D. DE BRUIN

SALBUTAMOL AND BECLOMETHASONE INCHRONIC ASTHMA

SIR,-Dr Clarke and Dr Anderson (July 8, p. 70) haveattempted to show that inhalation of bronchodilator aerosol 30min before beclomethasome dipropionate (B.D.P.) improves theaccess of the latter to the bronchi, thereby improving its effect.Unfortunately the design of the study prevents analysis of thisvery point.The authors conclude that salbutamol/beclomethasone aero-

sol combination produces better control in chronic asthmathan B.D.P. alone. If this is true it could just as well be due tothe effect of salbutamol as a bronchodilator per se, rather thanto any enhanced effect of B.D.P. It might have been preferableto compare two periods, during which both B.D.P. and salbuta-mol were used, but in a different order-i.e., salbutamol given30 min before and 30 min after-rather than to compare

B.D.P./placebo with B.D.P./salbutamol. In addition, since therewas no period in which salbutamol was used without B.D.P. onecannot say whether the use of salbutamol with B.D.P. was anymore beneficial than salbutamol alone.

Thoracic Out-patients Department,Llandough Hospital,Penarth CF6 1XX

P. D. J. HANDSLIPJ. P. R. HARTLEY

TERMINAL DEOXYNUCLEOTIDYL TRANSFERASEIN HUMAN TONSILS

SIR,-The presence of terminal deoxynucleotidyl transfer-ase (TdT) in the thymocytes and precursor T cells is wellestablished. 1-3 In an attempt to assign some biological role forthis enzyme, Baltimore’ suggested that TdT acts as a somaticmutagen which is responsible for the production of diversifiedimmunoglobulins. Since the antibody response is elicited byboth B and T lymphocytes, it was logical to assume that B pre-cursor cells would also contain TdT or similar enzyme. Balti-more et al.1 found a putative B-cell TdT (the enzymerequired a template and would incorporate mismatched nuc-leotide). We tested chicken bursa and human tonsil extracts forthis putative specialised D.N.A. polymerase and found no

enzyme activity.’ In chicken bursa, D.N.A. polymerase P has anunusually high rate of mismatched nucleotide incorporationand may qualify as a mutagenic D.N.A. polymerase.? D.N.A.polymerases from human tonsil extracts did not exhibit anymutagenic property, but in some human tonsils (6 out of 22)we found, to our surprise, low levels of TdT.A typical phosphocellulose chromatogram of a tonsil extract

is shown in the figure. Tonsil enzyme has been found to beidentical to classical TdT with respect to divalent cation and

primer requirement, response to sulphydryl inhibitors, and

1. Kung, P C , Gottlieb, P. D., Baltimore, D. J. biol. Chem. 1976 251, 2899.2 Bollum, F J. Proc natl Acad Sci. U.S.A. 1977, 74, 734.3. Bollum, F J. ibid p. 3993.4 Baltimore, D. Mature, 1974, 248, 4095. McCaffrey, R., Smoler, D. F., Baltimore, D. in Modern Trends in Human

Leukemia edited by R. Neth, R. C Gallo, S. Spiegelman, F. Stohlman,Jr.i,p.247 New York, 1974.

6 Baltimore, D, Silverstone, A. E , Kung, P D., Harrison, T. A., McCaffrey,R. P Cold Spring Harb. Symp. Quant. Biol. 1976, 63

7 Modak, M. J., Bhatt, H., Seidner, S., Hahn, E., Gupta, S., Good, R. A. Bio-chem. Biophys Res. Commun. (in the press).

Froction number

Phosphocellulose chromatography of tonsil extract.

20 ul of each fraction were assayed either in the presence (-) or absence of50 fLmol/1 A.T.P. (t-). A.T.P. is a selective inhibitor of TdT.’ (0-0) representsa TdT-negative sample of tonsil. Samples were obtained from children at tonsil-lectomy for chronic tonsilar enlargement and were stored at -70°C in "tris"buffered glycerol (10"( v/v).

Extraction and partial purification of TdT using phosphocellulose chroma-tography and determination of enzyme activity was essentially as described

before 8 "’

inhibition by the TdT-specific inhibitor A.T.P. (table).8 9 Inaddition, chromatographic behaviour on phosphocellulose andmolecular weight of the enzyme, as judged by glycerol gradientcentrifugation, are indistinguishable from those observed withA.L.L.-derived TdT (data not shown).’O The total amount ofactivity present in tonsil tissue of this size (3 g) is equivalentio 10-7 bone-marrow cells obtained from a normal donor or5 x 10-5 thymocytes when assayed under our conditions.

Distribution of various classes of lymphocytes in tonsils isknown.ll Tonsillar tissues contained 50-75% B cells as definedby the presence of surface immunoglobulins using (Fab’)2 anti-immunoglobulin reagents. 30-50% of the cells were mature Tlymphocytes as defined by their rosette formation with sheeperythrocytes. There was a small proportion of cells whichlacked both classical B and T cell surface markers. These so-called third population or "null" cells contain precursors of Blymphocytes: 12 Since both mature T and B lymphocytes havebeen rigorously shown not to contain TdT, the presence ofTdT in tonsil tissue may then be attributed to the third popu-

8. Bhalla, R. B., Schwartz, M., Modak, M. J. ibid, 1977, 76, 1056.9. Modak, M. J. Biochemistry, (in the press).10 Marcus, S. L., Smith, S. W., Jarowsky, C., Modak, M. J. Biochem. Biophys.

Res. Commun. 1976, 70, 3711. Gupta, S., Pahwa, R., Siegel, F., Good, R. A. Clin. exp. Immun. 1977, 28,

347 12. Chess, L., Schlossman, S. S. in Contemporary Topics in Immunology (edited

by N. Warner), p 363 New York, 1977