ABSTRACT
<p><b>OBJECTIVE</b>To explore the immune response of silicotic rats to sheep red blood cells(SRBC).</p><p><b>METHODS</b>Silicotic rats were immunized with SRBC by tracheal instillation(Group 1) or intraperitoneal injection (Group 2), and non-silicotic rats were immunized by tracheal instillation as normal control(Group 3). The levels of serum hemolytic index(HC50) were measured on 7, 12, 20, 25, and 32 days after primary immunization and 5, 12, 15 days after the second immunization. Special anti-SRBC IgG was measured with ELISA(A490 nm) on 12, 20, 25, 32 days and 5, 12, 15, 27 days respectively. Delayed-type hypersensitivity(DTH) to SRBC was measured 20 days after second immunization and DTH reaction was determined at 24, 48, 72, and 96 h after administration. Total cell count and cell populations in the bronchoalveolar lavage fluid(BALF), lung associated lymph node(LALN) and spleen weight, special IgG secreted from spleen cells were measured at the end of the experiment.</p><p><b>RESULTS</b>The HC50 of Group 1(47.4 +/- 1.0, 52.2 +/- 4.6, 31.1 +/- 11.9, 43.8 +/- 3.5, 33.6 +/- 16.8, 49.0 +/- 2.3, 92.9 +/- 20.2, 87.7 +/- 5.2) were statistically higher than those of Group 3(40.4 +/- 10.6, 2.8 +/- 2.5, 0.8 +/- 0.6, 6.6 +/- 5.8, 1.4 +/- 0.1, 36.5 +/- 16.5, 53.0 +/- 33.2, 2.6 +/- 2.2). The special anti-SRBC IgG response in Group 1(1.67 +/- 0.19, 1.98 +/- 0.36, 1.12 +/- 0.50, 1.38 +/- 0.30, 2.75 +/- 0.15, 2.60 +/- 0.28, 2.86 +/- 0.10, 2.50 +/- 0.20) were much stronger than those in Group 3 (0.59 +/- 0.30, 0.56 +/- 0.21, 0.21 +/- 0.16, 0.22 +/- 0.01, 0.81 +/- 0.25, 0.74 +/- 0.25, 0.69 +/- 0.26, 1.38 +/- 0.41). Furthermore, the results of DTH showed positive response and the ratios for diameter of skin rash > 5 mm at 24, 48, 72, 96 h were 16/16, 16/16, 16/16, 15/16 respectively in Group 1, while those in Group 3 were 8/15, 1/15, 1/15, 1/15 respectively. Total cell count in the BALF, LALN and spleen weight, and special IgG secreted from spleen cells in Group 1 were higher too. Group 2 expressed almost of the same but with mild immunologic responses as Group 1.</p><p><b>CONCLUSION</b>Silicosis-induced extremely strong DTH and over-response of humoral immunity to some antigens may contribute to the likelihood of silicosis complicated with tuberculosis.</p>