Guinea Pig-Adapted Foot-and-Mouth Disease Virus with Altered Receptor Recognition Can Productively Infect a Natural Host

Abstract

We report that adaptation to infect the guinea pig did not modify the capacity of foot-and-mouth disease virus (FMDV) to kill suckling mice and to cause an acute and transmissible disease in the pig, an important natural host for this pathogen. Adaptive amino acid replacements (I 248 3T in 2C, Q 44 3R in 3A, and L 147 3P in VP1), selected upon serial passages of a type C FMDV isolated from swine (biological clone C-S8c1) in the guinea pig, were maintained after virus multiplication in swine and suckling mice. However, the adaptive replacement L 147 3P, next to the integrin-binding RGD motif at the GH loop in VP1, abolished growth of the virus in different established cell lines and modified its antigenicity. In contrast, primary bovine thyroid cell cultures could be productively infected by viruses with replacement L 147 3P, and this infection was inhibited by antibodies to ␣v␤6 and by an FMDV-derived RGD-containing peptide, suggesting that integrin ␣v␤6 may be used as a receptor for these mutants in the animal (porcine, guinea pig, and suckling mice) host. Substitution T 248 3N in 2C was not detectable in C-S8c1 but was present in a low proportion of the guinea pig-adapted virus. This substitution became rapidly dominant in the viral population after the reintroduction of the guinea pig-adapted virus into pigs. These observations illustrate how the appearance of minority variant viruses in an unnatural host can result in the dominance of these viruses on reinfection of the original host species.The high potential for adaptation and rapid evolution that derives from the quasispecies dynamics of RNA virus populations (30, 40) can be reflected in the alteration of cell tropism, host range, and virulence (8,9,30,43,51). Mutant viruses with a modified host range can contribute to the emergence of new animal and human diseases (62). On the other hand, adaptation to a new host has been exploited since the beginning of vaccinology to derive attenuated strains with decreased pathogenicity for the original, natural host (18).Foot-and-mouth disease virus (FMDV) belongs to the Picornaviridae family and is the etiological agent of the most important animal disease affecting domestic cloven-hoofed animals and a large variety of wild artiodactyls (for reviews, see references 2, 6, 21, 63, 68, and 74). The virus consists of a nonenveloped particle of icosahedral symmetry containing a positive-sense single-stranded RNA genome of about 8.5 kb. A single open reading frame encodes all of the capsid, as well as a total of nine additional mature, nonstructural (NS) proteins, including two proteases (L and 3C) and an RNA-dependent RNA polymerase (3D) (14,69,73). As shown for a number of different picornaviruses, the mature NS proteins, as well as some of their protein precursors, are involved in multiple functions needed for virus multiplication and the host cell membrane rearrangements associated with viral RNA replication (3,25,35,46,55,60,65,82).FMDV can initiate the infection of cultured cells via different ␣v integrins (␣v␤1,␣v␤...

Mutations That Hamper Dimerization of Foot-and-Mouth Disease Virus 3A Protein Are Detrimental for Infectivity

“…This result is consistent with the ability of the guinea pig-adapted virus carrying replacement Q44R to kill suckling mice and to cause acute disease in the pig (47). On the contrary, in cells transfected with RNA carrying the replacement Q44D, a delay in the production of infectious virus was observed and the recovered virus displayed replacement D44E.…”

“…An amount of 100 ng RNA from pMT28 killed 4 of the 5 animals injected, a lethality value similar to that reported for other FMDV RNAs derived from full-length infectious clones (7). RNA from pMT28-Q44R was also lethal for suckling mice, as 100 ng of RNA killed 3 out of 4 injected animals, and sequencing of the 3A coding region of RNA extracted from dead mice showed the presence of replacement Q44R, confirming the capacity of the virus carrying this mutation to infect suckling mice (47). Conversely, RNAs from pMT28Q44D, pMT28L38E, and pMT28L41E were not lethal at doses of RNA up to 10 5 ng ( Table 4), suggesting that these replacements allow viral replication in cultured cells, enabling selection of revertant mutants, and abolish viral multiplication in an animal model, such as suckling mice.…”

A Single Amino Acid Substitution in the Capsid of Foot-and-Mouth Disease Virus Can Increase Acid Lability and Confer Resistance to Acid-Dependent Uncoating Inhibition

“…In the case of the C-S8c1 virus, the pH 50 values were 6.58 to 6.60, very similar to those reported for type A FMDV (13). This indicates that an increase of only about 0.3 units of pH 50 resulted in complete resistance to NH 4 Cl. Mutants displaying intermediate pH 50 values (c1 and c3) escaped from the inhibitory effect of NH 4 Cl to a lesser extent.…”

“…This indicates that an increase of only about 0.3 units of pH 50 resulted in complete resistance to NH 4 Cl. Mutants displaying intermediate pH 50 values (c1 and c3) escaped from the inhibitory effect of NH 4 Cl to a lesser extent. FMDV uncoating is supposed to occur within early and recycling endosomes (8,52), and these are mildly acidic compartments (pH of about 6.5) (65).…”

“…3B). Mutant c2 was the most acid labile, with a pH 50 value (defined as the pH value leading to a 50% loss of infectivity) of 6.95. Mutants c1 and c3 displayed intermediate acid lability (pH 50 values of 6.70 for c1 and 6.78 for c3), between that of c2 and that of C-S8c1 (pH 50 of 6.58).…”