Virus-Neutralizing Activity Mediated by the Fab Fragment of a Hemagglutinin-Specific Antibody Is Sufficient for the Resolution of Influenza Virus Infection in SCID Mice

Abstract

Antibodies (Abs) contribute to the control of influenza virus infection in vivo by reducing progeny virus yield from infected cells (yield reduction [YR]) and by inhibiting progeny virus from spreading the infection to new host cells (virus neutralization [VN]). Previous studies showed that the infection could be resolved in severe combined immunodeficiency (SCID) mice by treatment with hemagglutinin (HA)-specific monoclonal antibodies (MAbs) that exhibit both VN and YR activities but not by MAbs that exhibited only YR activity. To determine whether virus clearance requires both activities, we measured the therapeutic activity of an HAspecific MAb (VN and YR) and its Fab fragment (VN) by intranasal (i.n.) administration to infected SCID mice. Immunoglobulin G (IgG) and Fab cleared the infection with i.n. 50% effective doses (ED 50 s) of 16 and 90 pmol, respectively. To resolve an established infection solely by VN activity, Fab must be present in the respiratory tract at an effective threshold concentration until all infected cells have died and production of virus has ceased. Because IgG and Fab had different half-lives in the respiratory tract (22 and 8 h, respectively) and assuming that both operated mainly or solely by VN, it could be estimated that clearance was achieved 24 h after Ab treatment when both reagents were present in the respiratory tract at ϳ10 pmol. This dose was ϳ200 times larger than the respiratory tract-associated Ab dose resulting from administration of the intraperitoneal ED 50 (270 pmol) of IgG. This indicated that our procedure of i.n. administration of Ab did not make optimal use of the Ab's therapeutic activity.

Antibody-Dependent Cell-Mediated Cytotoxicity- and Complement-Dependent Cytotoxicity-Independent Bactericidal Activity of an IgG against Pseudomonas aeruginosa O6ad

“…Thus, te-hS20 may have the best protective efficacy because it has the highest binding avidity and because it might further mediate bacterial elimination through Fc region-mediated effector functions such as phagocytosis (40). Furthermore, the longer in vivo t 1/2 (22-120 h) of intact IgGs in mice (72,73), when compared with those of Fab (4-8 h) (73) and scFv molecules (2-3.5 h) (74,75), also likely contributes to its better protective efficacy. Nonetheless, despite lacking the Fc region, the protection provided by the anti-O6ad Fab and scFv was clearly profound, adding strong support in demonstrating the bactericidal activity of these Abs independent of ADCC and CDC.…”

Influenza Type A Virus Escape Mutants Emerge In Vivo in the Presence of Antibodies to the Ectodomain of Matrix Protein 2

“…Unlike HA-specific Abs (22,25), M2e-specific Abs cannot prevent virus from initiating an infection or resolve an established infection, but they can diminish the yield of infectious virus and thus inhibit progression of the infection (23,31). We were interested in establishing an experimental system in which the growth-restricting activity of M2e-specific Ab and the capability of influenza virus to escape it could be best assessed in vivo.…”

Natural Antibody and Complement Mediate Neutralization of Influenza Virus in the Absence of Prior Immunity

“…We sought to determine whether enhanced complement deposition was associated with increased blockade of the viral receptor (HA). The availability of HA to be recognized by a neutralizing IgG2a antibody (H36-4-5.2) that binds to the Sb portion of HA (27) was examined after treatment with serum. Sera from RAG1 Ϫ/Ϫ mice alone reduced the binding of H36-4-5.2 to PR8 virus particles by 33% (Fig.…”

“…The H36-4-5.2 hybridoma produces a mouse IgG2a antibody that neutralizes PR8 virus by binding to the Sb/B site on HA (27). To obtain purified antibody, culture supernatants were precipitated by saturated ammonium sulfate precipitation.…”