Towards an in vitro model for acute hemorrhagic conjunctivitis: cytokine-mediated vascular endothelial cell activation triggered by enterovirus type 70 infection

BACKGROUND

Little is known of the pathogenetic mechanisms of enterovirus type 70 (EV70), a causative agent of acute hemorrhagic conjunctivitis. However, virus- or cytokine-induced perturbation of vascular endothelial cells are potential triggering events.

OBJECTIVE

To determine whether EV70 infection of human umbilical vascular endothelial cells (HUVECs) and human corneal epithelial cells (HCEs) causes the release of vasoactive cytokines, capable of triggering vascular endothelial cell activation.

STUDY DESIGN

Susceptibility of cultured HUVECs and HCEs to EV70 was tested by observing the appearance of cytopathic effect or immunoprecipitation of viral protein in infected cells. The culture fluids from the virus-infected cells were tested for their ability to stimulate the expression of intercellular adhesion molecule-1 (ICAM-1) on uninfected HUVECs. Anti-cytokine antibodies were used to identify ICAM-1-activating cytokine(s).

RESULTS

Both HUVECs and HCEs were susceptible to EV70 infection. Culture fluids from EV70-infected HUVECs and HCEs stimulated ICAM-l expression on uninfected HUVECs, which was completely blocked by anti-interleukin-1alpha (IL-1alpha) antibody but not by interleukin-1beta (IL-1beta) or anti-tumor necrosis factor alpha (TNFalpha) antibodies.

CONCLUSION

This study provides the first evidence of EV70 infection of both HCEs and HUVECs, and furthermore, identifies IL-1alpha as the predominant endothelial cell-activating factor produced by EV70-infected cells. Since endothelial cell activation is often an initiating step towards vascular permeability and/or inflammation, the perturbation of endothelial cell function through EV70 induced IL-1alpha is thus a potential contributory factor in the pathogenesis of EV70-associated hemorrhagic conjunctivitis.

Systemic and ocular antibody responses to inactivated acute hemorrhagic conjunctivitis (AHC) virus; enterovirus 70 (EV70)

PURPOSE

Evaluate the immune response in rabbits injected with EV70, the agent of acute hemorrhagic conjunctivitis (AHC) and AHC associated neuropathy.

METHODS

Rabbits were injected intramuscularly with uv-light inactivated EV70 isolate J670/71. Neutralizing activity against EV70 was quantified in serum and tear samples and the immunoglobulin (Ig) classes of the neutralizing activity in serum identified by sucrose gradient ultra-centrifugation. Adjuvant muramyl dipeptide (MDP) was applied topically to assess the role of ocular inflammation on levels of neutralizing antibody, proteins and Ig in tears. The protective effects of human and rabbit sera and interferon-alpha (IFN-alpha) against EV70 were compared in human conjunctival and lens cells.

RESULTS

Sera collected at 6 and 13 d contained 19S IgM anti-EV70 neutralizing antibody, while serum collected 21 d post injection contained 19S IgM and 7S IgG anti-EV70 neutralizing antibody. Low titers of anti-EV70 activity (< or =30 U/ml) were detected in tears of seropositive rabbits. MDP induction of conjunctivitis in seropositive rabbits increased tear IgG concentration (3-fold) and anti-EV70 neutralizing antibody titers (> or =10-fold). The protective effect of the rabbit and human sera against EV70 infection in conjunctival, but not lens epithelial cells, was enhanced by the addition of IFN-alpha.

CONCLUSIONS

Immunization with uv-light inactivated EV70 elicits a classical humoral immune response in rabbits. The protective activity of serum in EV70-infected human conjunctival cells, but not lens cells, was increased by IFN-alpha. Adjuvant MDP-induced conjunctivitis, increased blood-conjunctival barrier (BCB) permeability and anti-EV70 neutralizing activity in tear of seropositive rabbits. The results suggest immunization with inactivated EV70 could provide systemic as well as ocular protection during natural EV70 infection.

Acute hemorrhagic conjunctivitis due to enterovirus 70 in American Samoa: serum-neutralizing antibodies and sex-specific protection

Acute hemorrhagic conjunctivitis due to enterovirus 70 has caused extensive outbreaks in tropical areas since 1969. Between December 1, 1990, and March 4, 1991, an outbreak of acute hemorrhagic conjunctivitis due to enterovirus 70 occurred in American Samoa, where an outbreak due to the same agent had occurred in 1981. A survey of 5% of the households (134 households, 1,095 individuals) was conducted throughout the island of Tutuila. The outbreak affected 58% of the population, with age-specific attack rates greater than 50% for all age groups except children younger than 2 years. Attack rates were significantly higher for children 2-10 years old (65%) than in the remainder of the population. Women aged 21-40 years had higher rates than did men the same age (66 vs. 49%), possibly because of the close association of women and young children. At higher preepidemic titers, there was evidence of protection from clinical disease among males but not among females. Enterovirus 70 can cause large outbreaks even in a population already exposed in a previous large outbreak; protection due to previous infection is only partial.

[Rapid diagnosis of enterovirus 70 infection by detection of IgM antibodies with a biotin-avidin ELISA]

A biotin-avidin immunoassay was developed to detect IgM antibodies to enterovirus 70 (EV70) in sera from patients with acute hemorrhagic conjunctivitis. Biotinylated monoclonal antibody to EV70 and horseradish peroxidase-streptavidin were used in an indirect IgM capture ELISA. 40 acute- and convalescent-phase serum pairs were tested and 34 sera (85.0%) in the convalescent phase were positive for IgM antibodies. The positive rate of the method was much higher than that of the non-biotin-avidin system for EV70 (55%). Two sera in the acute phase, which were negative for neutralizing antibodies, had IgM antibodies. Two serum specimens which had been collected a third time from 2 patients during the seventh week after onset were positive for IgM, showing that EV70 IgM lasts at least for one month and a half. The biotin-avidin ELISA is sensitive and can be performed in 2 days instead of 3 days for the non-biotin-avidin method, and is useful for rapid diagnosis of EV70 infection.

Acute haemorrhagic conjunctivitis: seroepidemiology of coxsackievirus A24 variant and enterovirus 70 in Singapore

Epidemics of acute haemorrhagic conjunctivitis caused by a variant of coxsackievirus A24 (CA24v) and enterovirus 70 (EV70) have occurred periodically in Singapore. A seroepidemiological survey conducted before the CA24v epidemic in 1985 and in the midst of the EV70 epidemic in 1983 showed a neutralising antibody prevalence (greater than or equal to 1:4) of 19.1% and 66.9% to CA24v and EV70, respectively. The seropositivity rate to both viruses was highest in children 10-14 years of age, but no sex or ethnic difference was noted. It appears from the data that an epidemic could be triggered when the herd immunity of the population falls below a critical level. There was a significant correlation in seroprevalence between CA24v and EV70 (P = 7.75 x 10(-3).

An outbreak of acute haemorrhagic conjunctivitis in Kaduna, Nigeria

Clinical studies were carried out on two groups of patients with acute haemorrhagic conjunctivitis (AHC) during an epidemic in 1985 in Northern Nigeria. Group 1 consisted of 99 students attending a girls' boarding school, group 2 of 200 patients selected randomly from 1000 examined at the local clinic. Moderate to severe hyperaemia and papillary responses were present in the palpebral conjunctiva of all patients, and 234 (66%) had subconjunctival haemorrhages. Transient superficial punctate keratitis was noted in over 60% of patients. A transient flare suggestive of a low grade iritis was seen in five patients. No neurological disorders were noted. Serological studies were carried out on patients from group 2. Fifteen paired and 20 single serum samples were titrated against adenovirus type 4 (Ad-4) and enterovirus type 70 (EV-70). Two pairs of sera showed a 4-fold rise in antibody levels to EV-70, whereas the antibody titres to EV-70 in the rest of the sera ranged from 1:20 (no antibody) to 1:160. None of the paired serum samples showed a 4-fold rise in antibody levels to adenovirus. The results of clinical studies and serological findings support EV-70 as a probable cause of AHC in Nigeria.