Immune response in the absence of neurovirulence in mice infected with m protein mutant vesicular stomatitis virus

Abstract

Matrix (M) protein mutants of vesicular stomatitis virus (VSV), such as rM51R-M virus, are less virulent than wild-type (wt) VSV strains due to their inability to suppress innate immunity. Studies presented here show that when inoculated intranasally into mice, rM51R-M virus was cleared from nasal mucosa by day 2 postinfection and was attenuated for spread to the central nervous system, in contrast to wt VSV, thus accounting for its reduced virulence. However, it stimulated an antibody response similar to that in mice infected with the wt virus, indicating that it has the ability to induce adaptive immunity in vivo without causing disease. These results support the use of M protein mutants of VSV as vaccine vectors.

FIG. 1.

Immunohistochemical staining for VSV antigens in the nasal passages and brains of mice. Magnification, ×4. Images of the nasal passages of rwt and rM51R-M virus-infected animals at days 1, 2, 4, and 7 (D1, D2, D4, and D7, respectively) are shown in the top four rows of images. The images in the bottom row show the olfactory bulb region of the brain at day 7 postinfection (D7-OB). The inset images are shown at ×40 magnification. In the positive images (those with red staining), the epithelial surfaces of the nasal cavity show strong cytoplasmic and mucosal surface immunoreactivity. Similar staining is present in the olfactory bulb at day 7 with the rwt virus.

FIG. 2.

Hematoxylin- and eosin-stained histological sections of the nasal passages of VSV-infected mice at days 1, 2, and 4 (D1, D2, and D4, respectively) after infection with the rwt and rM51R-M viruses. Magnification, ×4. Magnification of inset images, ×40. Mild inflammation with hemorrhages and a few inflammatory cells are present in both at day 1. The injury progresses with the rwt virus from days 2 to 4, while there are no significant lesions with the rM51R-M virus by day 2. This further injury is characterized by mucosal ulceration, with epithelial sloughing and more intense luminal inflammation.

FIG. 3.

Immunohistochemical staining for VSV antigens in the lungs (A) and spleens (B) of mice 4 and 7 days postinfection (D4 and D7, respectively) with the rwt and rM51R-M viruses. Magnification, ×60. Positive cells (those with red staining) are scattered throughout both organs with the rwt virus and in all but the lungs at day 7 with the rM51R-M virus.

FIG. 4.

(A) Anti-VSV antibody titers in mice infected with the rM51R-M or rwt viruses. Mice were infected intranasally with the indicated doses of the rM51R-M or rwt viruses. Total serum Ig titers were determined by enzyme-linked immunosorbent assay (ELISA) using purified VSV as antigen. The symbols represent the titers of individual mice at 14 days postinfection, the bars represent geometric mean titers, and the numbers in parentheses represent the number of mice/total with titers above the negative control. (B) Weight change in mice infected with the rM51R-M or rwt virus. The data shown are the mean weights of the mice described in panel A infected with the rM51R-M virus at 10⁴ PFU (open squares), 10⁵ PFU (open circles), or 10⁷ PFU (open triangles) or the rwt virus at 10⁴ PFU (filled squares). (C and D) Anti-VSV IgG1 and IgG2a titers of mice infected with the rM51R-M or rwt virus. The data shown are the geometric means ± standard deviations of the results for five mice per group from a separate experiment from the one described in panel A.