Pandemic Swine-Origin H1N1 Influenza Virus Replicates to Higher Levels and Induces More Fever and Acute Inflammatory Cytokines in Cynomolgus versus Rhesus Monkeys and Can Replicate in Common Marmosets

<div><p>The close immunological and physiological resemblance with humans makes non-human primates a valuable model for studying influenza virus pathogenesis and immunity and vaccine efficacy against infection. Although both cynomolgus and rhesus macaques are frequently used in influenza virus research, a direct comparison of susceptibility to infection and disease has not yet been performed. In the current study a head-to-head comparison was made between these species, by using a recently described swine-origin pandemic H1N1 strain, A/Mexico/InDRE4487/2009. In comparison to rhesus macaques, cynomolgus macaques developed significantly higher levels of virus replication in the upper airways and in the lungs, involving both peak level and duration of virus production, as well as higher increases in body temperature. In contrast, clinical symptoms, including respiratory distress, were more easily observed in rhesus macaques. Expression of sialyl-α-2,6-Gal saccharides, the main receptor for human influenza A viruses, was 50 to 73 times more abundant in trachea and bronchus of cynomolgus macaques relative to rhesus macaques. The study also shows that common marmosets, a New World non-human primate species, are susceptible to infection with pandemic H1N1. The study results favor the cynomolgus macaque as model for pandemic H1N1 influenza virus research because of the more uniform and high levels of virus replication, as well as temperature increases, which may be due to a more abundant expression of the main human influenza virus receptor in the trachea and bronchi.</p></div

Radiographic score in cynomolgus macaques, rhesus monkeys and common marmosets in time.

<p>Both left and right lung lobes were scored from 0–3, giving a maximal radiographic score of 6 of the complete lung.</p

Body temperature of cynomolgus macaques, rhesus macaques and common marmosets before and after Mex4487 influenza virus infection.

<p>(A) Circadian temperature pattern, shown for two animals of each species (C5, C6, R5, R6, M5 and M6). The circadian pattern was calculated from the temperatures recorded during three weeks before infection. Grey areas represent the mean temperature with the 95% confidence interval. (B) Body temperature increase during infection. Shown is the net-increase in temperature, which was calculated by subtracting the individual circadian body temperature from the actually recorded temperature in time after infection. Data are depicted from the two animals of each species that were maintained in study for 14 days (C5, C6, R5, R6, M5 and M6). (C) Cumulative net temperature increase, calculated as area under the curve (AUC) from the net-increase data, either for the first 3.5 days or the first 6.5 days of infection. Colored dots represent individual animals (green: CRM1, orange: CRM2, red: CRM3, light blue: CRM4, purple: CRM5, dark blue: CRM6). C: cynomolgus, R: rhesus, M: marmoset. Statistical differences between groups were determined with Mann-Whitney test.</p

Quantification of intensity of 56 kD band in SNA staining on SDS-PAGE of trachea and bronchus tissue samples from cynomolgus and rhesus monkeys.

<p>Indicated is the intensity of signal as percentage of signal from 62kD band of Fetuin (positive control).</p><p>Quantification of intensity of 56 kD band in SNA staining on SDS-PAGE of trachea and bronchus tissue samples from cynomolgus and rhesus monkeys.</p

T-cell activation in cynomolgus and rhesus macaques after Mex4487 influenza virus infection.

<p>Shown is the percentage of CD4 T-cells (left graphs) and CD8 T-cells (right graphs) expressing CD69, CD25 or Ki-67 for each individual animal in time.</p

Lymphocyte, neutrophil and monocyte counts in blood of cynomolgus and rhesus macaques after Mex4487 influenza virus infection.

<p>Shown are the absolute counts (10⁹ cells/liter whole blood) for each individual animal in time after infection with Mex4487 influenza virus at day 0.</p

Clinical score of cynomolgus macaques, rhesus macaques, and common marmosets.

<p>For each individual animal the total clinical score is shown in time after infection with Mex4487 influenza virus at day 0.</p