Application of lectin and B-lymphocyte-specific monoclonal antibodies for the demonstration of human microglia in formalin-fixed, paraffin-embedded brain tissue.

To evaluate the usefulness of microglial markers for routine neuropathological material, we studied formalin-fixed, paraffin-embedded human brain tissue with the immunoperoxidase method using the lectin Ricinus communis agglutinin (RCA-1) and four monoclonal antibodies (LN-1, LN-2, LN-3, anti-HLA-DR/alpha). RCA-1 stained resting microglia, but the staining intensity was mostly weak. LN-1 also stained resting microglia in paraffin sections first treated with protease. In contrast to LN-1, RCA-1 stained blood vessels heavily. LN-1 stained resting microglia more markedly than RCA-1 in brains fixed for a prolonged period of time. However, LN-1 recognized a small number of astrocytes in routine paraffin sections. LN-3 reactivity was detected on a few resting microglia, but was intensely expressed on large numbers of reactive microglia in many neurological diseases. Both LN-2 and anti-HLA-DR/alpha labelled microglia, but the reactions were inconsistent. This study suggests that the monoclonal antibodies LN-1 and LN-3 are useful for the demonstration of microglia in paraffin sections, and a combination of these antibodies and the antibody to glial fibrillary acidic protein is recommended in attempting to identify microglia.