MDCK-SIAT1 cells show improved isolation rates for recent human influenza viruses compared to conventional MDCK cells

Abstract

The ability to isolate and propagate influenza virus is an essential tool for the yearly surveillance of circulating virus strains and to ensure accurate clinical diagnosis for appropriate treatment. The suitability of MDCK-SIAT1 cells, engineered to express increased levels of alpha-2,6-linked sialic acid receptors, as an alternative to conventional MDCK cells for isolation of circulating influenza virus was assessed. A greater number of influenza A (H1N1 and H3N2) and B viruses from stored human clinical specimens collected between 2005 and 2007 were isolated following inoculation in MDCK-SIAT1 cells than in MDCK cells. In addition, a higher titer of virus was recovered following culture in MDCK-SIAT1 cells. All A(H1N1) viruses recovered from MDCK-SIAT1 cells were able to agglutinate both turkey and guinea pig red blood cells (RBC), while half of the A(H3N2) viruses recovered after passage in MDCK-SIAT1 cells lost the ability to agglutinate turkey RBC. Importantly, the HA-1 domain of the hemagglutinin gene was genetically stable after passaging in MDCK-SIAT1 cells, a feature not always seen following MDCK cell or embryonated chicken egg passage of human influenza virus. These data indicate that the MDCK-SIAT1 cell line is superior to conventional MDCK cells for isolation of human influenza virus from clinical specimens and may be used routinely for the isolation and propagation of current human influenza viruses for surveillance, diagnostic, and research purposes.

FIG. 1.

Isolation and passaging of influenza virus samples in MDCK and MDCK-SIAT1 cells. Human clinical specimens and cell- and egg-passaged influenza virus samples were cultured in duplicate in MDCK or MDCK-SIAT1 cells for 4 days. The supernatants were collected, and influenza virus titers were measured by TCID₅₀ assay. (A) Total number of human clinical virus isolates recovered in each cell line. N.R., samples not recovered; SIAT1, MDCK-SIAT1 cells. (B) Recovery of A(H3N2) viruses from stored clinical samples by year of collection. (C) Titers for individual stored clinical samples (average of duplicates) isolated in either MDCK (black) or MDCK-SIAT1 (white) cells. (D) Titers for viruses previously isolated in eggs (squares) or MDCK cells (diamonds) and repassaged in MDCK (black) or MDCK-SIAT1 (white) cells. The medians are indicated by the horizontal bars. *, P < 0.001; **, P < 0.005; ***, P < 0.0005.

FIG. 2.

RBC agglutination after cell culture. Human clinical specimens cultured in MDCK or MDCK-SIAT1 cells were assayed by hemagglutination assay with either guinea pig or turkey RBC. Shown are the numbers of hemagglutination-positive samples (titer > 1) for each RBC type from MDCK- or MDCK-SIAT1-cultured A(H1N1) (white) or A(H3N2) (black) viruses. I/C, incomplete agglutination (thus, the titer was not determined).