The non-haemadsorbing African swine fever virus isolate ASFV/NH/P68 provides a model for defining the protective anti-virus immune response

Abstract

African swine fever virus ASFV/NH/P68 is a naturally occurring, non-haemadsorbing and non-fatal isolate. Longitudinal clinical and immunological studies on 31 pigs inoculated oronasally or intramuscularly with this isolate defined two discrete groups of animals : those developing ASF chronic type lesions and those remaining asymptomatic. Animals developing lesions had viraemia and fever late after infection, NK activity levels close to that of control animals and high levels of anti-ASFV specific antibodies together with a marked hypergammaglobulinaemia involving IgG1, IgG2, IgM and IgA immunoglobulin isotypes. Pigs remaining asymptomatic after infection, on the other hand, did not have viraemia or fever after day 14 post-infection and had elevated NK cell activity, but normal plasma Ig concentrations and relatively low specific anti-virus antibody concentrations throughout the duration of the experiments. Importantly, the latter group of pigs virus were resistant to subsequent challenge with the highly virulent ASFV/L60 isolate and survived with no major changes in any of the parameters examined and referred to above. Finally, lymphoproliferative responses to the mitogens concanavalin A, phytohaemagglutinin and pokeweed mitogen were not depressed in either of the two clinically defined groups of pigs. Thus further studies with this infection model may provide new insights on mechanisms of protective immunity to ASFV.

In vivo depletion of CD8+ T lymphocytes abrogates protective immunity to African swine fever virus

“…As a number of porcine lymphocyte subpopulations express CD8 on their surface, the next question was which CD8 + lymphocyte subpopulation(s) plays a role in the protective immune response to ASFV infection. In young pigs, a large proportion of CD8 + lymphocytes are NK cells (Yang & Parkhouse, 1996, 1997) and a possible contribution of NK cells in the immune response to ASFV infection was suggested by Leitao et al (2001). However, very low levels of NK cells were seen in these experiments, as the combined number of CD8b + and CD4 + CD8 + lymphocytes was roughly the same as the total CD8 + lymphocyte population (Figs 2 and 3).…”

“…The presence of ASFV-specific cytotoxic T lymphocytes has been demonstrated (Martins et al, 1993); these are CD8 + and MHC class I-dependent and may recognize VP32 (Martins et al, 1993;RamiroIbanez et al, 1997;Jenson et al, 2000). Other studies have described high levels of IFN-c production by ASFV-immune lymphocytes stimulated in vitro with ASFV (Revilla et al, 1992) and elevated natural killer (NK) cell activity during infection (Leitao et al, 2001); however, 3Present address: Instituto Gulbenkian de Ciencia, 2780-156 Oeiras, Portugal. Fig.…”

African swine fever: how can global spread be prevented?

“…Protection can be achieved by inoculation of pigs with low-virulence isolates obtained by passage in tissue culture or by deletion of genes involved in virulence, as well as low-virulence isolates from the field (Lewis et al 2000;Leitao et al 2001;Boinas et al 2004). The mechanism of protection involves cell-mediated immunity, since depletion of CD8þ T cells abrogates protection (Oura et al 2005;Denyer et al 2006).…”

New insights into the role of ticks in African swine fever epidemiology

“…The deletion of specific genes has been assayed several times (56,57,58) but more information on ASFV pathogenicity is required to guide the selection of appropriate virulence genes for deletion. Attempts to create replication-deficient vaccines that contain all the external particles of the virus but are not infectious are also in progress.…”