Virology research and virulent human pandemics.

The possibility that a devastating human pandemic could arise, causing massive loss of human life, is discussed. Such a major threat to the human species is likely to be a virus, and would spread by the respiratory route. It need not necessarily cause massive loss of life, but if it caused serious illness or incapacity it would still have a major impact. A possible source is from an existing respiratory pathogen, but it would more probably arise from an infection that is maintained in an arthropod or vertebrate host, but which at present either does not infect humans, or if it does it fails to be effectively transmitted between them. More research should therefore focus on the pathogenetic factors and the viral determinants that promote respiratory transmission.

The Zvonimir Dinter Memorial Lecture. New insights into the pathogenesis of viral infection.

Interesting recent highlights into the pathogenesis of viral infections have come from: (1) Studies of viruses that persist in cells and modify cell function without causing cell damage. (2) Transgenic mouse studies showing how tissue-specific transcriptional activators control virus expression and can determine viral tropism. (3) Studies of the influence of cell differentiation on viral expression. (4) The exploding world of cytokines, whose baffling complexity and multiple interactions are subjects of intense study. (5) Studies of the interaction of viruses with the immune system. In each case, no molecular studies are giving unprecedented insights into disease processes. However, even when viral genomes are sequenced and virulence genes identified there are additional daunting steps before we understand the role of a given gene product in pathogenesis.

Studies of depressed interleukin-2 production by spleen cells from mice following infection with cytomegalovirus.

Spleen cells from mice infected with virulent and avirulent strains of murine cytomegalovirus showed depressed interleukin-2 production after ConA stimulation. Cell-mixing experiments indicated that this was due to a primary defect in non adherent cells. Spleen cells infected in vitro were also studied.

Genetic basis for Ia positivity and susceptibility to lactic dehydrogenase virus in macrophages of SJL/J mice.

SJL/J mice showed a higher elevation of serum lactic dehydrogenase after lactic dehydrogenase virus (LDV) infection, and a higher per cent of Ia positive and LDV infectable cultured macrophages, than several other mouse strains. Genetic studies suggested that these unique characteristics in SJL/J mice are closely linked and inherited as a single autosomal recessive trait, which is not within the H-2 gene complex.

DMSO induces reactivation of cytomegalovirus in vitro from spleens of latently infected mice. Brief report.

Reactivation of murine cytomegalovirus in spleen explant cultures from latently infected CD 1 mice was studied. A significant increase in the incidence of reactivation was observed when 200 mM DMSO was included in the culture medium. Virus could also be reactivated from the bone marrow of some mice.

Live lactate dehydrogenase-elevating virus (LDV) induces suppressor T cells that inhibit the development of delayed hypersensitivity to LDV.

A strong delayed-type hypersensitivity (DTH) response to lactate dehydrogenase-elevating virus (LDV) in mice was induced by immunization with u.v.- or heat-inactivated virus by the intravenous, intraperitoneal and especially the subcutaneous route. The peak DTH response was seen 7 days after immunization. Live virus, in contrast, did not induce a DTH response in young (1- to 3-month-old) mice irrespective of inoculation route, except after pretreatment with cyclophosphamide (CY), when the response peaked at 14 days. Live virus, however, induced a significant DTH response in old mice (greater than 8 months) without CY. The DTH response to inactivated virus was reduced when live virus was given intraperitoneally at the same time, but was partially restored when Ia-positive peritoneal cells were also given intravenously. The DTH response induced in infected mice pretreated with CY was suppressed by injection of spleen cells from infected or from normal 1- to 3-month-old mice. Suppression by normal spleen cells was abolished by treatment with anti-Thy1.2, anti-Lyt1 and anti-Lyt2 plus complement, whereas suppression by spleen cells from infected mice was prevented by anti-Thy1.2 and anti-Lyt2 plus complement. It is concluded that suppression of the DTH response was associated with induction of suppressor T cells and that severe depletion of Ia-positive cells may also have played a part.

Subclass distribution of IgG and IgA responses to rubella virus in man.

Monoclonal anti-subclass antibodies were used in a micro-ELISA method to determine rubella-specific IgG subclass antibodies in serum from 22 subjects who had acute rubella or had been vaccinated, from 10 infants with congenital rubella, and in serum and synovial fluid samples from 21 patients with chronic arthritis. In nearly all samples IgG1 was the only type of IgG antibody detected. In acute infections it was present within 10 days of the onset of the rash. IgG4 antibody was detected in sera from two immune individuals. Rubella-specific IgA1 subclass antibody was detected by the same technique in sera from 6 of 12 subjects with acute rubella as early as 3 days but not later than 28 days after the appearance of the rash.

Viral infection in patients with multiple sclerosis and HLA-DR matched controls.

Retrospective comparisons of the prevalence and age, where appropriate, of some childhood infectious illnesses and vaccinations, together with serological evidence for exposure to 16 viruses, many of which have previously been implicated in the aetiology of multiple sclerosis (MS) were made in 177 patients with acute optic neuritis, other recent isolated demyelinating episodes or established MS and 164 controls. The expected high frequency of HLA-DR2 in patients with demyelinating disease was matched by preselection of normal controls with this antigen (DR2+); the remaining individuals were classified as HLA-DR2 negative/DR3 positive (DR3+) or HLA-DR2 and 3 negative (DR2/3 -). Cases were compared with controls, collectively and in analyses restricted to each genetic group; these comparisons were repeated considering the three categories of patients with demyelination and two control populations separately. All DR2+, DR3+ and DR2/3 - individuals were compared in a single analysis to assess the effect of HLA type itself on the results. Patients with demyelinating disease had rubella and measles at a later age and reported mumps infection more frequently than controls. Age of typhoid vaccination and duration of exposure to domestic dogs was higher in all cases than controls. Age of measles and mumps, but not rubella, was higher in DR2+ cases than controls; but differences were not observed in the other genetic groups. Higher rubella antibody titres were present in all cases than controls and in analyses confined to DR2+ individuals in whom higher Epstein Barr virus antibody titres were also present. Measles haemagglutination inhibition and parainfluenza I antibody titres were increased and influenza A antibodies detected less frequently in all patients with optic neuritis and those with DR2 compared with appropriate controls; influenza B antibody titres were lower in all DR2+ cases than controls. Higher adenovirus and varicella zoster antibody titres were present in DR2/3- patients with demyelination and other neurological diseases compared with normal controls. Overall, older age of infection and higher antibody titres were observed more often in patients with optic neuritis, in particular DR2+ cases, than other individuals with demyelination or controls. Our serological results are consistent with the presence of abnormal HLA-immunological reactivity in patients with MS but cannot be explained only by an effect of DR type itself; age at which susceptible individuals develop some common childhood infections may also influence the subsequent development of the disease.

Infection of mice with lactic dehydrogenase virus prevents development of experimental allergic encephalomyelitis.

A significant reduction in the incidence of experimental allergic encephalomyelitis (EAE) in SJL/J mice was observed when mice were infected with lactic dehydrogenase virus (LDV) 14 days before, on day 0, or 3 days after immunization with spinal cord homogenate. These results are discussed in terms of the selective infection by LDV of I-region-associated antigen- (Ia) positive macrophages.

Alopecia in mice infected with murine cytomegalovirus (MCMV).

When mouse cytomegalovirus was injected subcutaneously into 4-12 day old CDI mice there was infection of dermal cells and the dermal papillae of hair follicles. Infected cells were never seen in the epidermis nor in the epithelium of hair follicles. When larger doses of virus (5 X 10(4) pfu) were given, dermal infection led to gross necrosis of the skin, ulceration, scabbing and healing with alopecia. Smaller doses (10(4) pfu) did not cause gross necrosis but damage to follicles resulted in alopecia or sparse hair growth. Skin lesions were not seen after infection of 4-8 week old mice, even when the inoculated skin area had been epilated, or when hyaluronidase was mixed with the virus inoculum. These experiments show that cytomegalovirus, in contrast to herpes simplex and varicella-zoster viruses, infects dermal but not epidermal cells, and that dermal tropism is age-restricted.

Synthesis of antibodies, including antiviral antibodies, in the knee joints of patients with arthritis.

Serum and synovial fluids from 16 patients with seronegative arthritis and eight with rheumatoid arthritis were studied for immunoglobulin levels and for antibody levels to five viruses. When allowances were made for the distribution of immunoglobulins between serum and synovial fluid there was evidence that in several patients antibody to one or more viruses was synthesised locally in the joint. IgG and especially IgM were present in greatly increased amounts in arthritic joints compared with normal joints. On the basis of serum/synovial fluid ratios inflammation and local immunoglobulin synthesis are discussed as possible causes. These results are compared with antiviral antibody and immunoglobulin ratios observed in the serum and cerebrospinal fluid of patients with multiple sclerosis.

Ia antigens and Fc receptors of mouse peritoneal macrophages as determinants of susceptibility to lactic dehydrogenase virus.

The relationship between susceptibility of mouse peritoneal macrophages to lactic dehydrogenase-elevating virus (LDV) infection and expression of I region-coded antigens (Ia) on these cells was investigated. The proportion of Ia-positive cells in resident peritoneal macrophages from adult and suckling mice were 4 to 10% and 50 to 70% respectively. Approximately the same percentage of the cells were susceptible to LDV, as detected by fluorescent antibody staining. In adult mice, double-labelling experiments showed that most of the Ia-positive cells were LDV-infected. When the cells were cultured for more than 24 h in vitro, Ia-positive cells rapidly disappeared and the culture became resistant to LDV. Removal of Ia-positive cells by treatment with anti-Ia plus complement or enrichment using an anti-Ia-coated Petri dish simultaneously removed or enriched for LDV-susceptible cells. Treatment of cells with trypsin (1 mg/ml) removed their I-A and I-E antigens and simultaneously abolished susceptibility for LDV. When LDV was preincubated with subneutralizing amounts of antibody, infectivity for macrophages was enhanced and the proportion of LDV-infected cells was higher than that of Ia-positive cells. This suggests that Fc receptors on macrophages can act as receptors for LDV coated with antiviral IgG.