Submitted to: Great Lakes International Imaging and Flow Cytometry Association
Publication Type: Abstract Only
Publication Acceptance Date: 9/28/2006
Publication Date: 9/28/2006
Citation: Kimura, K., Vincent, A.L., Richt, J.A., Lager, K.M., Roth, J.A., Kehrli, Jr., M.E. 2006. Effect of vaccination and/or challenge of swine influenza virus on the proportion of activated cells in bronchoalveolar lavage fluid [abstract]. Great Lakes International Imaging and Flow Cytometry Association. Paper No. 7.
Technical Abstract: Swine influenza, caused by influenza A virus (SIV), is described as an acute respiratory disease with a high morbidity in pigs. Killed vaccines that contain both H1N1 and H3N2 subtypes are available commercially; however, due to recently emerging novel subtypes and genetic/antigenic variants, effective management of SIV remains a challenge. We have tested whether the use of NS1-truncation mutant, based on the TX98 (H3N2) strain as a modified live vaccine (MLV), might protect pigs from SIV infection with wild type TX98, an antigenically distinct H3N2 (CO99), or the heterosubtypic H1N1 (IA04) isolates. We investigated whether protection was associated with the activation and recruitment of lymphocytes in bronchoalveolar lavage fluid (BALF). Seventy SIV negative pigs (5 weeks old) were divided into 8 groups as shown in Table I. Three weeks after intranasal vaccination with the MLV, pigs were boosted with a second dose of the MLV. Two weeks after the boost, pigs were challenged intratracheally with one of three SIV isolates and euthanized 5 days after challenge. BALF was obtained at necropsy and lymphocyte populations were examined by flow cytometry for the expression of CD44, CD18, CD4, CD8, N4 (TCR-1), IgM, MHC-II, and CD25. Vaccination induced complete protection from challenge with wild type TX98, nearly complete protection from CO99, and partial protection from IA04. Without vaccination, pigs with TX98 challenge had the lowest percentage of pneumonia lesions, followed by CO99. The IA04 challenged pigs had substantially greater percentages of lung involvement. BALF from challenged pigs contained significantly more lymphocytes when compared to the non-challenged controls. In our assays, CD44highCD18high, CD25+ cells, and CD4+CD8+, MHC-II+ T-cells are considered “activated”. A lower CD4/CD8 ratio indicated an increase in CD8+ cells, which are thought to be important for immune protection of the host from virus infections. The CD4/CD8 ratio was very low in Groups 2 (0.11 +/- 0.05), 3 (0.11 +/- 0.02), and 6 (0.08 +/- 0.04), followed by Groups 1(0.26 +/- 0.02), 7 (0.48 +/- 0.05), 8 (0.69 +/- 0.11), 4 (0.71 +/- 0.07) and then 5 (1.36 +/- 0.16). Vaccination decreased the CD4/CD8 ratio, thus increased the migration of CD8+ cells into the lung. In addition, a pattern of increased CD44highCD18high cell percentage of total lymphocytes was observed in vaccinated pigs. Within the CD8+ lymphocyte population, these percentages were TX98>CO99>>IA04. They increased in MLV-vaccinated, TX98- and CO99-challenged pigs (80.2 +/- 2.0 % and 68.8 +/- 3.9 %, respectively) when compared to non-vaccinated TX98 and CO99 challenged pigs (63.0 +/- 3.7 % and 58.3 +/- 2.8 %, respectively). However, the percentages were nearly equal in IA04 non-vaccinated or vaccinated and challenged pigs (38.0 +/- 4.9 % vs. 35.6 +/- 6.0 %). A similar pattern was observed in other activation marker expressions. However there was no effect of MLV-vaccination on CD44highIgM+ cells. The percentage of activated non-B cells tended to correlate with the degree of protection. These results suggest that the degree of recruitment and activation of lymphocytes, especially CD8+ cells, are associated with the protection from the SIV-induced damage. Virus specific CD8+ cells might be involved in the immune protection induced by the MLV.