A possible role of pre-existing IgM/IgG antibodies in determining immune response type

On the basis of the data indicating the existence of two types of immuno-protection, namely macrophage-mediated and mast cell-basophil-mediated, it is argued that by reacting with potential pathogens, pre-existing IgM and IgG antibodies (both natural and induced by environmental microflora) might promote involvement of macrophages in the presentation process, favouring the generation of pathogen-specific T helper 1 (Th1), but not Th2, responses. Alternatively, the failure of these antibodies to effectively recognize pathogens might be associated with active involvement of pathogen-specific B cells in presenting Ag and, as a consequence, with the predominant development of Th2, rather than Th1, responses.