Abstract
In the present study toxicity and immunostimulating activity of the lectin(KML-C), which was extracted from Korean mistletoe(Viscum album coloratum) were investigated in swine. To determine the toxicity, lectin was injected into thigh or cervical muscles of 4-week-old piglets(Landrace) and observed clinically and pathologically. For determination of the immnunostimulating activity, lectin($0.7{\mu}g/kg$ of body weight)-adjuvanted vaccine of Aujeszky's disease virus(ADV)(NYJ1-87) which was inactivated by 0.2% formalin was injected into the cervical muscle of antibody-negative piglets in the same age group. Subpopulation of the immune cells and serum neutralizing(SN) antibodies in the piglets were examined after vaccination, and resistance of the piglets against challenge by virulent NYJ1-87 was further examined. The results were also compared with those from piglets injected with aluminum hydroxide [$Al(OH)_3$]-adjuvanted vaccine of inactivated NYJ1-87 and NYJ1-87 vaccine without adjuvant, and the results are as follows. By injection of lectin with $30{\mu}g/kg$ of body weight to the thigh muscle, all of 12 piglets died after signs such as dyspnea, fever, systemic erythema and subcutaneous hemorrhages, and lesions pertaining to poisonous hepatitis and dysfunction of kidney were observed. By injection of lectin with $7{\mu}g/kg$ of body weight to the thigh muscle, all of 12 piglets showed signs such as edema and cutaneous hemorrhage in the injected area, lameness and depression, and lesions pertaining to poisonous hepatitis and dysfunction of kidney were observed. By injection of lectin with 1, 3 and $5{\mu}g/kg$ of body weight to the thigh muscle of each one piglet, signs such as congestion, induration and grayish coloration in the injected area, depression and inappetence were observed in all piglets. Toxic changes were also observed in the liver and kidney of piglets by lectin of 3 and $5{\mu}g$. By injection of lectin with 0.5 and $0.7{\mu}g/kg$ of body weight to the cervical muscle of each 9 piglets, all piglets were clinically normal and there were no significant changes in blood counts and chemistry values. Whereas, epithelial swelling and vacuolation of convoluted tubules were observed from one piglet injected with lectin of $0.7{\mu}g$, and necrosis and fibrosis of muscular fiber were observed in the muscle of one piglet injected with lectin of $0.5{\mu}g$. Only population of sIgM+ B lymphocytes increased among immune cells in all of 15 piglets immunized with lectin($0.7{\mu}g/kg$ of body weight)-adjuvanted vaccine, while compared to those in $Al(OH)_3$-adjuvanted vaccine and vaccine without adjuvant. No additional stimulation to the immune cells was recognized when lectin was added to $Al(OH)_3$-adjuvanted vaccine. In piglets immunized with lectin-adjuvanted vaccine, SN titers in reciprocal values for loge were 1.3-4.0 at 1-4 weeks after vaccination, which was similar to those with 1.0-3.3 by vaccine without adjuvant but lower than those with 2.0-5.7 by $Al(OH)_3$-adjuvanted vaccine. Also, no additional increase in the SN titers was recognized when lectin was added to $Al(OH)_3$-adjuvanted vaccine. Piglets immunized with lectin-adjuvanted vaccine were resistant to challenge by the virulent NYJ1-87 at 4 weeks after vaccination, and the SN titers reached to 5.0 one week after challenge, which was higher than those with 4.0 by vaccine without adjuvant but somewhat lower than those with 7.7 by $Al(OH)_3$-adjuvanted vaccine.
