Casein Protein Block to Optimize Immunohistochemistry Detection of Surface Immunoglobulin Heavy Chain Expression in Lymphoid Cells

We describe our recent experience of studying expression of immunoglobulin (Ig) heavy chain (IgG, IgM, and IgA) in lymphoid cells comprising a research set of formalin-fixed, paraffin-embedded human diffuse large B-cell lymphoma samples. We found that using typical clinical automated immunohistochemistry protocols and usual buffers as blocking agents, the extent of undesirable staining was extreme and impaired our ability to interpret heavy chain Ig expression by individual lymphoid cells. We were not able to optimize this with serial dilutions in antibody concentration or time of primary antibody exposure. We therefore developed an added step of casein protein block, which solved the problem. We are not aware of other such reports in clinical or human research tissue sets and believe this solution may be useful when clinical pathologists or researchers encounter similar technical issues.