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Many microorganisms gain access to the systemic circulation after entering the respiratory tract. The precise pathways used to cross the mucosal barriers of the lungs have not been clearly described. We have used the mammalian reoviruses in order to determine the pathway that a systemic virus uses to penetrate the mucosal barrier and enter the systemic circulation after entering the airways of the lungs. Reoviruses enter through pulmonary M cells, which overlie bronchus-associated lymphoid tissue, and subsequently spread to regional lymph nodes. Thus, the pathway through M cells represents a strategy by which viruses and probably other microorganisms can penetrate the mucosal surface of the respiratory tract and thereby enter the systemic circulation.

A syngeneic monoclonal antiidiotypic antibody was generated in BALB/c mice after repeated immunization with a BALB/c monoclonal anti-reovirus hemagglutinin (HA) antibody. The resultant syngeneic monoclonal antiidiotypic antibody, in the absence of adjuvant, was found to be capable of priming both BALB/c (H-2d, Igh-1a) and C3H/Hej (H-2k, Igh-1j) mice for Lyt-1+- and Lyt-2+-dependent responses against the mammalian reovirus. By the use of intertypic reassortants and variant virus analysis, the specificity of the response was finely mapped to the neutralization domain of the viral hemagglutinin (HA). Using purified monoclonal antiidiotype, we were able to compare the potency of antiidiotype to virus in terms of induction of immunity. 8 X 10(8) protein molecules were able to prime for cellular responses to reovirus. These studies indicate that in the reovirus system, T cells and B cells share idiotypic configurations, and that antiidiotypic antibodies of the type described herein may be useful in the development of vaccines against certain viral infections.

A xenogeneic antiserum raised to antireovirus immunoglobulin was used to define an idiotypic determinant present on antibodies to reovirus type 3 hemagglutinin. The same idiotype was identified on nonimmune lymphoid cells and on neuronal cells that specifically bind the hemagglutinin of type 3 reovirus. This idiotypic determinant, called Id3, is shared by (a) a monoclonal antibody to the neutralization site of hemagglutinin from type 3 reovirus; (b) BALB/c serum antibodies to the hemagglutinin of reovirus type 3; (c) R1.1, a murine thymoma cell line that binds reovirus type 3; (d) primary cultures of murine neuronal cells. The presence of an idiotype shared by antihemagglutinin antibodies and by structures on nonlymphoid cells suggests a general relationship between disparate receptors that recognize a common determinant. Furthermore, this suggests a novel approach for the study of viral receptor interactions and for analysis of mechanisms of autoimmune responses.

The mammalian reoviruses provide a model for studying specific aspects of the immunopathogenesis of viral infection. We have used two serotype 3 reoviruses to define stages in the pathogenesis of central nervous system (CNS) infection at which a mAb specific for the reoviral cell attachment protein sigma 1 (sigma 1mAbG5) acts to protect mice against lethal disease. sigma 1mAbG5 administered either before or at the time of footpad inoculation with reovirus T3D prevented entry of T3D into the CNS. sigma 1mAbG5 also inhibited the spread of reovirus T3C9 from the gastrointestinal tract to the CNS after peroral inoculation with T3C9. These effects occurred in the absence of a significant effect of sigma 1mAbG5 on primary replication in skeletal muscle (T3D) or the gastrointestinal tract (T3C9). sigma 1mAbG5 administered after T3D had reached the spinal cord inhibited subsequent spread of infectious virus from spinal cord to brain. Even after direct intracerebral inoculation of T3D, sigma 1mAbG5 prevented both growth in the brain and spread of infectious virus from brain to eye, spinal cord, and muscle. Treatment with sigma 1mAbG5 after intracerebral inoculation with T3D prevented neuronal necrosis and resulted in a delayed and topographically restricted inflammatory response. We detected no antibody-resistant T3D variants in vivo after treatment with sigma 1mAbG5. We conclude that systemic IgG does not play a significant role at the primary site of infection with reoviruses, while it clearly acts to prevent infection of the CNS and extension of infection with the CNS. Further study will be directed to defining what components of the immune system do act at primary sites of infection, and to defining the mechanisms by which antibody acts at defined stages in pathogenesis.

The mammalian reoviruses (serotype 1, strain Lang and serotype 3, strain Dearing) differ in their sensitivity to digestion by chymotrypsin. We have found that the M2 double-stranded RNA (dsRNA) genome segment (encoding the micro1C outer capsid polypeptide) is responsible for this property. In addition to determining response to protease treatement in vitro, we have found that the M2 genome segment also determines the ability of these two viruses successfully to initiate local and systemic infection in newborn mice after peroral inoculation. Thus the M2 dsRNA segment defines a new virulence gene of the mammalian reoviruses.

The S1 genome segment of reovirus is linked to type specificity as determined by neutralization antibody. This gene segment codes for a minor outer capsid polypeptide (sigma1). Therefore, sigma1 is the peptide responsible for induction of neutralization antibody and confers type specificity. This biologic property of reovirus was defined using hybrid recombinants clones between reovirus types 1 and 3 and 2 and 3.