Abstract
The primary in vitro response to fowl IgG (FGG) of spleen cells from congenitally athymic (nu/nu) mice was used as a model of antigen‐induced bone marrow‐derived (B) lymphocyte activation. Functional evidence was presented that deaggregated FGG (De‐FGG) bound rapidly to B lymphocytes at 0 °C, an antibody‐forming cell (AFC) response to FGG occurring if the spleen cells, after washing off of unbound FGG, were subsequently cultured in the presence of polymerized flagellin (POL). This supported the concept that antigen can induce B cell triggering without being presented in a multivalent form.
Conversely, De‐FGG could not be demonstrated by functional studies to bind to spleen cell suspensions at 37 °C so as to initiate subsequent triggering in the presence of POL. In fact, FGG which had bound at 0 °C became ineffective in B cell triggering if the spleen cells were briefly incubated at 37 °C before being washed and cultured with POL. However, if cells were incubated for 60 min at 37 °C with FGG in the presence of POL, washing of the cells did not prevent a significant response in the absence of further additions of FGG. When cells that had been incubated for 60 min at 37 °C with FGG and POL were treated with trypsin and were cultured without the addition of further POL or FGG, a significant anti‐FGG antibody‐forming cell response still occurred. This implied that activation of some B cells had proceeded within 60 min to a stage independent of further extracellular antigen. It was shown that this initial activation proceeded independent of the presence of fetal calf serum.
An additional observation was that when cells that had been incubated at 37 °C with FGG plus POL were treated with trypsin after they had been washed, the subsequent anti‐FGG response was reduced compared to that of cells that had merely been washed. Possible mechanisms for this effect are considered.