Association between cytokine profile and disease severity in children infected with respiratory syncytial virus causing lower respiratory tract infection
Montlha, Mahlodi Petunia
Background: Respiratory Syncytial Virus (RSV) is a common cause of upper and lower respiratory tract infections (LRTI), primarily in children having severe disease manifestation. In South Africa, RSV is identified in approximately 25-30% of children hospitalized for LRTI. There is a spectrum of RSV-associated LRTI severity. Understanding associations between immune mediators and RSV-LRTI severity could assist clinicians in the triaging for level of care. Several cytokines have been implicated in RSV-LRTI severity. Aim: Study the associations between cytokine levels from plasma and nasopharyngeal aspirate with RSV infection or RSV-associated LRTI severity in hospitalized infants ranging from 0-12 months of age. The correlation between plasma and nasopharyngeal aspirate cytokine concentrations was also evaluated. Methods: Paired plasma and nasopharyngeal aspirate (NPA) samples were collected from polymerase chain reaction confirmed RSV-infected infants without coinfection with other pathogens that we investigated for. Paired samples were also collected from RSV negative-control infants (n=31) who did not have any respiratory symptoms. Control-infants were scheduled for elective surgery; samples were collected before administration of medication and surgical procedure. RSV associated LRTI episodes were grouped into mild (n=89) and severe RSV-LRTI (n=113) using the Respiratory Index of Severity in Children (RISC) Score. Interferon gamma (IFN-γ), interleukins (IL) IL-1α, IL-1β, IL-4, IL5, IL-6, IL-8, IL-9, IL-10, IL-12(p70)IL-13, macrophage inducing protein (MIP-1α), monocyte chemo attractant protein (MCP-1), tumour necrosis alpha (TNF-α), Regulated on activation, normal T cell expressed and secreted (RANTES) and were measured with multiplex immunosorbent assay using Luminex® technology. Cytokine profiles were evaluated for association of RSV-LRTI severity and between RSV LRTI cases and controls. Results: Comparing hospitalized RSV-associated LRTI to control infants, RSV cases had elevated plasma TNF-α (0.7pg/ml vs. 0.5pg/ml; p=0.007), and IL-10 (1.0pg/ml vs. 0.6pg/ml; p=0.02) concentrations, and reduced plasma MIP-1α (12pg/ml vs. 28pg/ml; p=0.008) and IFN-γ (3pg/ml vs. 5pg/ml; p=0.02) levels. Nasopharyngeal aspirate TNF-α (8.0pg/ml vs. 1.0pg/ml; p=0.01), IL-8 (2682pg/ml vs. 184pg/ml; p=0.002), MCP-1 (287pg/ml vs. 66pg/ml; p<0.001), MIP-1α (27pg/ml vs. 6.7pg/ml; p=0.004) concentrations were elevated in RSV-LRTI cases compared to control infants. Infants hospitalized with severe RSV-associated LRTI (RISC score ≥2) were younger than mild cases (3.9 vs. 4.5 months; p=0.01). In RSV cases, severe RSV-LRTI was associated with increased plasma IFN-γ levels (4pg/ml vs. 3pg/ml) and NPA MIP-1α concentrations (88pg/ml vs. 50pg/ml, mean; all other values medians) compared to mild RSV-LRTI. In a multivariate analysis, NPA MIP-1α levels remained associated with RSV-LRTI (p=0.05), but could not predict RSV-LRTI severity. Conclusion: This study observed that during RSV-associated LRTI, immune response was directed at the respiratory tract. Reduced concentrations of plasma IFN-γ and elevated levels of cytokines in the NPA may suggest that the blood of RSV-LRTI cases had reduced number of IFN-γ producing cells. There was no evidence of distinct Th1 or Th2 type immune response and the cytokines associated with RSV-LRTI severity could not predict the outcome of severe RSV-associated LRTI. Key words: Respiratory Syncytial Virus, Lower respiratory tract infections, Severity, Plasma, Nasopharyngeal aspirate, IFN-γ, MIP-1α, Luminex®
A dissertation submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Medicine in the field of Clinical Microbiology and Infectious Diseases Johannesburg, 2018.