Methods for producing antibodies are provided and include transforming a plant cell with a nucleic acid encoding a heavy chain of an antibody, a light chain of an antibody, and a linking polypeptide connecting the heavy chain to the light chain. The nucleic acid is then expressed in the plant cell, such that, upon expression the linking polypeptide is cleaved to separate the heavy chain from the light chain. Isolated nucleic acid sequences, expression vectors, and transformed plant cells useful for producing the antibodies are also provided. Further provided are methods for treating a viral infection and include the steps of obtaining an antibody produced by the above-described methods and then administering the antibody to a subject.