Abstract: The present invention relates to a method of detecting the presence of an antibody to an avian influenza hemagglutinin antigen in a sample from a subject, wherein the antibody binds to an epitope of an avian influenza hemagglutinin antigen, comprising the steps of cloning a nucleic acid encoding an avian influenza antigen into a vector, infiltrating a plant cell with the vector, recovering the antigen from the plant, contacting the sample with the antigen, and detecting the formation of an antibody-antigen complex, wherein the antibody-antigen complex comprises antibodies in the sample bound to the antigen and wherein the formation of an antibody-antigen complex confirms that the subject has been exposed to an avian influenza hemagglutinin antigen. The present invention also relates to a device for assaying the presence of an antibody to avian influenza hemagglutinin antigen in a sample from a subject.