Antigen 60 (A60), a member of the thermostable macromolecular antigen family (TMA) and main component of old tuberculin and purified protein derivative (PPD), has been purified from the cytoplasm of Mycobacterium bovis BCG; its structure and metabolism have already been described. In the present paper, the action of A60 on humoral immunity has been analysed by an ELISA type immunoassay, and that on cellular immunity by the mouse footpad swelling test. Injection of very low A60 doses into unprimed mice produced an undetectable level of anti-A60 antibodies; the effect of a booster inoculation was not appreciable in the absence of incomplete Freund's adjuvant, but was evident when the latter was added. Higher doses of the antigen produced an appreciable primary response, and a sharp and long-lasting secondary response, which had a 10-fold higher intensity in the presence of incomplete adjuvant. No detectable delayed hypersensitivity reactions were observed in unprimed mice after footpad injection of A60, whereas clear responses were elicited in primed mice. This effect was more pronounced when the footpad was injected after a secondary response than after a primary response, and it was invariably magnified by incomplete adjuvant. It is concluded that A60 is a powerful immunogen, which is able to induce primary and secondary responses and delayed hypersensitivity reactions, effects that are adjuvant-modulated and develop concurrently.

Cerebrospinal fluid (CSF) and serum samples from eight patients with bacteriologically proven (6) An A60-based ELISA-type immunoassay has been developed for serological analysis of tuberculosis in humans (Baelden et al, unpublished). The use of A60 as a new tuberculin for cutaneous testing has been proposed.2' In this study, an immunoblotting method was applied to CSF and paired sera samples of patients with TM. Using this test the intrathecal synthesis of oligoclonal anti-mycobacterial IgG antibodies was followed. In addition, immunoblotting experiments were performed in parallel with whole mycobacterial homogenates and with the purified antigen A60, to explore the importance of this antigen in the case of intrathecal mycobacterial infection.Patients (table 1) We studied eight patients (six females, two males; seven white, one oriental; age: 141-53 years), six of them with bacteriologically proven and two with clinically suspected TM. Three patients were also affected by lung