We tested the MAbs 2B12 and 2D1 for therapeutic efficacy in a nonlethal mouse model of wt CA04 virus infection (9
). Female BALB/c (8-week-old) mice were inoculated intranasally with 1,000 50% median infective dose (MID50
) units in a 50-μl volume of the CA04 virus, as described previously (13
). At 24 h after inoculation, mice were administered 200, 20, or 2 μg (approximately 10, 1, or 0.1 mg/kg) of MAb 2D1 or 2B12 or an equal volume of human IgG (Sigma) by the intraperitoneal route to each mouse, in groups of nine mice. Mice were observed for weight loss every other day for 14 days. Subsets of four animals treated with the MAbs were euthanized on day 3 after infection, and whole lungs were homogenized in 1 ml of sterile PBS. Virus titer in lung tissue homogenates was determined by plaque titration in MDCK cell monolayer cultures. The limit of virus detection was 100.95
. MAb 2D1 showed a marked therapeutic efficacy when administered 1 day after virus inoculation, resulting in a 5 log10
PFU/ml decrease of lung virus titers of lung homogenate at the highest dose (Table ) and the prevention of weight loss (Fig. ). MAb 2B12 did not affect replication in vivo
at the doses tested.
Therapeutic efficacy of 1918 HA-specific MAbs against replication of 2009 A(H1N1) virus in mice
FIG. 1. Therapeutic efficacy of 1918 HA-specific MAbs against disease caused by the 2009 A (H1N1) virus in mice. In each group, five mice were followed every other day for weight. MAb 2D1 at 200-μg or 20-μg doses prevented weight loss at all time (more ...)
Recent studies have described some novel antibodies that recognize influenza viruses across subtypes (3
). This report is the first to describe naturally occurring human MAbs to conserved HA sequences across two pandemic viruses. Antigenic sites are defined as regions for which the binding of specific antibodies is not affected by residue changes at neighboring sites (15
); however, overlap between sites can occur (1
). Our data suggest that the MAb 4D20 epitope overlaps both the Sa and the Cb sites and that its lack of affinity to novel H1N1 is due to changes within or adjacent to the Cb site. The Cb site was defined previously by amino acid residues 78, 79, and 80 and residues 81 to 83 of the HA (17
). The variability in residue 77 and the 4D20 binding data shown here suggest that this flanking residue also contributes to the Cb antigenic site. The involvement of the residue 125C in recognition of the 2009 virus by MAb 2B12, as found in a MARM we isolated, also reveals extension of the Sa antigenic site beyond conventional definitions. These data suggest that the 2D1 MAb may be promising for diagnostic or therapeutic purposes. However, prophylactic or therapeutic use of a single MAb directed to a site that is often variable in viruses circulating in humans should be considered with caution.