12th Ljudevit Jurak International Symposium on
Comparative Pathology
June 1-2, 2001

***F.J. Salguero, *P.J. Sanchez-Cordón, *M.J. Bautista, **C.P. Sanchez, A. Núñez, *J.C. Gómez-Villamandos
*Department of Veterinary Pathology, University of Córdoba, Cordoba, Spain
**CISA-INIA, Valdeolmos, Madrid, Spain
INTRODUCTION & AIM: Lymphocyte apoptosis is one of the most typical changes in acute African Swine Fever (ASF). Monocyte-macrophages are the main target cells of AFS virus, and moreover the main cells producing several cytokines such as TNF-, IL-1 and IL-6. In this work we correlate the infection of macrophages with the expression of these cytokines and lymphocyte apoptosis in experimental acute ASF.
MATERIALS & METHODS: 21 piglets were inoculated with ASF virus strain Spain-70 and killed at 1-7 post-inoculation days. 3 non-inoculated piglets were used as controls. Samples of spleen, thymus and lymph nodes were taken and fixed in different solutions. These samples were embedded in paraffin wax and Epon 812 and were processed routine for histopathology and ultrastructural studies. Immunohistochemistry was applied to detect ASF virus, TNF-, IL-1, IL-1, IL-6, and SWC3. TUNEL technique was applied to detect apoptosis. ELISA commercial kits were used to determine serum levels of TNF- and IL-1.
RESULTS: Infection of macrophages was detected at 1 pid in the spleen and 2 pid in the thymus and lymph nodes. The number of positive cells against the studied cytokines increased to 2 pid in the spleen and 3 pid in the thymus and lymph nodes. The number of macrophages in the lymphoid structures of the studied organs increased at the same dates. Lymphocyte apoptosis detected by 
electron microscopy and TUNEL technique increased to 2 pid and to a very severe  5 pid in the lymphoid structures. TNF and IL-1 levels in sera increased to 2 pid.
CONCLUSIONS: Lymphocyte apoptosis was evident in infected animals and coincide with ASF virus replication of environmental macrophages. Moreover, lymphocyte apoptosis was observed near macrophages expressing all the studied cytokines, that can produce apoptosis in different cell population (changes described for other diseases). Cytokine expression coincides  in space and in time with viral replication in macrophages and lymphocyte apoptosis, so we conclude that these phenomenas are a consequence of cytokine production induced by viral replication.
CONCLUSION: The increase of vascular permeability, responsible for the alveolar oedema characteristic of the acute form of the disease, and the apparition of neutrophil secuestration and fibrin microtrombi in septal capillaries coincided with the peak expression of IL-1 and TNF- by PIMs,  and these occur before the observation of the peak in  viral replication in these cells.
Poster Presentation