Abstract:

Objective To evaluate the effect of 11 Mycobacterium tuberculosis (MTB) antigens on the evaluation of skin reactions of MTB-sensitized guinea pigs. Methods The 18 specific pathogen free (SPF) guinea pigs (female, weight: 250-300 g) were selected and divided into three groups of high dose (5 μg), medium dose (0.5 μg) and low dose (0.1 μg), with 6 guinea pigs per group. The guinea pigs were sensitized with MTB strain (H37Rv, ATCC27294). After successful sensitization, the guinea pigs were intracutaneously injected with TB-PPD, EC and 11 MTB antigens (including recombinant antigen Rv3872, MPT64, Rv1985c, Rv0222, Rv3117, Rv3120, Rv2346c, Rv3619c, Rv3425, Rv1738 and Rv2626c), 0.1 ml for each. The transverse and longitudinal diameters of swelling in injection sites were recorded at 24 h and 48 h after injection, and the average diameter of induration ((transverse diameter+longitudinal diameter)/2) was calculated, the average diameter ≥5 mm was defined positive. The differences in skin reactions of 11 MTB antigens compared with TB-PPD and EC were analyzed. Results After 24 h of antigen injection, the positive rates of Rv3120 and Rv3619c were 9/9 and 8/9, respectively at the dose of 5 μg; the skin reactions of EC and MPT64 were all positive at the dose of 0.5 μg. In the skin reactions, the average diameters of induration (M(Q₁, Q₃)) of TB-PPD (at the dose of 5 IU), EC (at the dose of 0.5 μg), MPT64 (at the dose of 0.5 μg), Rv3120 (at the dose of 5 μg) and Rv3619c (at the dose of 5 μg) 24 h after injection were all significantly bigger than those 48 h after injection (the average diameter of induration (9.00 (7.00, 11.00) mm vs. 6.50 (5.50, 8.25) mm, 13.00 (12.75, 14.25) mm vs. 9.00 (8.00, 9.75) mm, 9.50 (8.50, 12.50) mm vs. 8.50 (5.50, 9.50) mm, 8.50 (6.25, 9.25) mm vs. 5.00 (0.00, 5.50) mm and 6.50 (5.50, 8.25) mm vs. 3.50 (1.50, 4.75) mm; Z values were -2.494, -2.677, -2.207, -2.673 and -2.670, respectively; P values were 0.013, 0.007, 0.027, 0.008 and 0.008, respectively). At the 24 h skin reaction, the average diameter of induration of MPT64 (at the dose of 0.5 μg), Rv3120 (at the dose of 5 μg) and Rv3619c (at the dose of 5 μg) were all similar to that of TB-PPD (at the dose of 5 IU), with no statistical difference (H values were -0.496, 0.819 and 1.714, respectively; P values were 1.000, 1.000 and 0.865, respectively). The sizes of skin reactions between MPT64 (at the dose of 0.5 μg) and EC (at the dose of 0.5 μg) were similar, with no significant difference (H=2.288, P=0.221). The average diameter of induration of Rv3120 (at the dose of 5 μg) and Rv3619c (at the dose of 5 μg) were both significantly smaller than that of EC (at the dose of 0.5 μg) 24 h after injection (H values were 3.795 and 4.690, respectively; P values were 0.001 and 0.000, respectively). Conclusion The skin reaction of MPT64 (at the dose of 0.5 μg) and Rv3120 (at the dose of 5 μg) in guinea pigs were relatively better and showed great potential in the diagnosis of tuberculosis.

Key words: Mycobacterium tuberculosis, Antigens, Skin tests, Evaluation studies