R. Kulshreshtha

JAPANESE ENCEPHALITIS VIRUS LATENCY IN PERIPHERAL BLOOD LYMPHOCYTES AND RECURRENCE OF INFECTION IN CHILDREN

In a study group of 40 children who had been admitted to hospital with acute encephalitis, the disease was due to infection with Japanese encephalitis virus (JEV). Three children developed recurrence of disease 8‐9 months later. No virus had been isolated from these three patients during the acute stage of their illness, but virus was recovered from all during the recurrence phase by co‐cultivation of their peripheral blood mononuclear cells in primary mouse embryo fibroblast cultures. Virus was also recovered by co‐cultivation of peripheral blood mononuclear cells collected 8 months after their acute disease from three out of eight randomly selected asymptomatic children within the study group but not from similar cultures set up from JEV‐seronegative children used as controls. Virus was also isolated by co‐cultivation of T lymphocytes of asymptomatic children as detected by indirect immunofluorescence or by inoculation in mice.

Secretion of the chemokine interleukin-8 during Japanese encephalitis virus infection

Japanese encephalitis (JE) virus infection induces infiltration of neutrophils in neural as well as extraneural tissues in patients. As interleukin-8 (IL-8) has inflammatory properties, the present study was undertaken to investigate the IL-8 concentrations in cerebrospinal fluid (CSF) and serum from patients with JE and correlate them with neutrophil counts. IL-8 was measured in the CSF or serum of 30 patients with confirmed JE. The majority (92%) of the acute CSF samples showed raised levels of IL-8 with raised numbers of polymorphonuclear leucocytes. Similarly, significantly higher serum IL-8 concentrations were detected in the acute phase of illness than in convalescent JE patients or normal healthy controls. Twenty-one of 25 patients with high concentrations of IL-8 showed significantly increased neutrophil counts in acute phase sera. A gradual decline in neutrophil counts was observed in the convalescent phase of patients who recovered. There was a significant correlation between IL-8 level and the severity of illness, as all severely ill and fatal cases showed higher levels of IL-8 in acute CSF or serum than the levels found in those who recovered. IL-8 concentrations remained high for a longer period in patients with prolonged severe illness than in those who made a complete recovery.

Evidence for latency of Japanese encephalitis virus in T lymphocytes

Activation of latent Japanese encephalitis virus (JEV) in the spleen has been studied by co-cultivation with allogeneic or syngeneic cells. Activated virus was isolated by co-cultivation from T lymphocytes of spleen, as shown by indirect immunofluorescence or by inoculation into mice. The B lymphocytes and macrophages of latently infected mice did not reactivate the virus. A higher proportion of Lyt 1 cells than Lyt 2 cells were harbouring JEV as shown by indirect immunofluorescence. The spleen cells from latently infected mice elicited the lymphoproliferative response but this was much lower than that observed in the controls. These findings suggest the establishment of latent JEV infection in T lymphocytes.

An enzyme immunoassay for detection of Japanese encephalitis virus-induced chemotactic cytokine

Japanese encephalitis virus (JEV) induces human peripheral blood monocytes to secrete a chemotactic cytokine [human macrophage-derived factor (hMDF)] which causes chemotaxis of neutrophils. The only known assay for hMDF cannot quantify its level in samples, so an enzyme immunoassay has been standardized for detection of hMDF and hMDF-specific antibodies in test samples. The reported enzyme linked immunosorbent assay (ELISA) was found to be sensitive (89%), specific (91%), accurate (92.2%) and reproducible and was able to detect a minimum concentration of 23 ng hMDF/ml in test samples. The chemotactic factor could be detected in JEV inoculated mouse sera and JEV infected culture fluids. Significant finding of the test was the detection of hMDF in sera of human cases of JE.