Mechanism of Enhanced Humoral Response in Rodents by a Synthetic Polymer

We previously reported that administration of a low molecular weight (MW=800) synthetic polymer, NED 137, significantly increases humoral and cellular immune responses in the rat. The effect of NED 137 on the murine humoral response to T-dependent (TD) and T-independent (TI) antigens was studied in C57 BL/6, CBA/J and Balb/c mice. The TD antigens (SRBC, DNP-DA with adjuvant) or TI antigen (DNP-Ficoll) were administered simultaneously with NED 137. The polymer significantly increased the direct PFC response to all antigens tested in normal mice. However, it could not restore the PFC response to SRBC in athymic (nu/nu) mice. The effect of NED 137 on accessory cells was studied by the assessment of the in vitro response to SRBC in normal and macrophage-depleted rat spleen cultures. The polymer stimulated both, the primary and secondary IgM response and its immunopotentiating activity was the greatest in macrophage-depleted spleen cell preparations. The lack of effect of NED 137 in systems devoid of functional T cells, dependency on and specificity for a sensitizing antigen and its ability to stimulate a secondary response suggest that this polymer does not act as a “conventional” B-cell polyclonal activator.