LP Cells : CD20
Immunophenotype of Lymphocyte-predominant (LP) Cells: LP cells are positive for CD45, CD45RA, CD45RB, and CD45RC, but are negative for CD45RO. They stain for pan B-cell markers such as CD20, CD22, and CD79a (variable), but not CD19. LP cells are also immunoreactive for CD40, CD70, CD74, CD80, and CD86. Positivity for J-chain confirms the B-cell origin of LP cells. B-cell transcription factors such as PAX5, BOB1, OCT1, and OCT2 are generally positive in LP cells. There is variable expression for PU.1 and IRF4 (MUM1). BCL6 - a key regulator of germinal center B cell program - is consistently positive. CD30 is negative but may sometimes be weakly positive. A potential diagnostic pitfall is the strong CD30-positivity in parafollicular immunoblasts found outside the B-cell nodules. CD15 and CD10 are negative in LP cells. This CD20 immunostain shows positivity in LP cells (large cells with strong membrane staining). The background is rich in T-cells (CD20-negative) and also contains a few reactive B lymphocytes (small CD20-positive cells).