Peanut Agglutinin (PNA) Binding as a Marker for Immature Human B Lymphocytes. Is Bone Marrow not the Complete Bursa-Equivalent?

Abstract

To investigate the nature of peanut agglutinin (PNA) binding cells in various human lymphoid tissues a double marker assay was performed using fluorescent PNA and rosetting with anti-μ or anti-δ coated ox red blood cells for detection of B cells or rosetting with sheep red blood cells for detection of T cells.

In human bone marrow 60.5 ± 8.6% of the surface µve (sµ+ve) B cells did bind PNA whereas only a small minority of the surface δ+ve (δ+ve) B cells (5.0 ± 4.2%) and none of the T cells were PNA+ve. In peripheral blood most of the PNA+ve cells appeared to be monocytes. Only a small proportion of the su+ve B cells (9.7 ± 2.7%) and none of the sδ+ve B cells or T cells did bind PNA. Contrarily in tonsils a relatively high proportion of sµ+ve B cells (33.2%) of sδ+ve B cells (26.3%) and of T cells (17.2%) were PNA+ve.

These results indicate that PNA binding is also a marker for immature B cells. Moreover in human bone marrow at least two populations of B cells may be distinguished, an immature population of sµ+ve, sδ-ve, PNA+ve B cells and a mature populations of sµ+ve, sδ+ve, PNA-ve B cells, the latter probably representing recirculating B cells. We hypothesize that the first population comprises immature B cells, that leave the bone marrow in an early stage and complete the maturation to immunocompetent B cells in peripheral lymphoid organs like tonsils.