The invention is directed to β1-6 glucans, compositions, diagnostic kits, and devices comprising the same, and methods of use thereof in modulating immune response and treating, delaying progression of, reducing the incidence or severity of cancer, infection, inflammation, and autoimmune diseases. The β1-6 glucans of certain embodiments of the invention are enriched for O-acetylated groups and/or conjugated to a solid support or linked to a targeting moiety. The β1-6 glucans of certain embodiments of the invention recruit immunoglobulin G antibodies to mediate complement and neutrophil killing. The conjugated β1-6 glucans of certain embodiments of the invention are targeted to cells to stimulate the immune response at the target location by activating complement-mediated lysis and recruitment of neutrophils.
