This invention provides a composition comprising an effective amount of glucan capable of enhancing efficacy of antibodies. This invention further provides the above compositions and a pharmaceutically acceptable carrier. This invention also provides a method for treating a subject with cancer comprising administrating the above-described composition to the subject. This invention provides a composition comprising effective amount of glucan capable of enhancing efficacy of vaccines. This invention also provides a method of treating a subject comprising administrating the above pharmaceutical composition to the subject. This invention provides a composition comprising effective amount of glucan capable of enhancing efficacy of natural antibodies. This invention provides a composition comprising effective amount of glucan capable of enhancing host immunity. This invention also provides a composition comprising effective amount of glucan capable of enhancing the action of an agent in preventing tissue rejection.