Fluorescence light micrograph of antibody- producing plasma cells in tissue from mouse spleen. These cells are producing two types of antibody protein: the red stained are secreting G (IgG), & the green stained immunoglobin M (IgM). No cell is stained both red & green, indicating the specificity of the immune response. They specialise in producing one sort of antibody only. Antibodies to IgM were labelled with the green dye fluorescein & antibodies to IgG with the red dye rhodamine. The labelled antibodies then bound selectively to cells with the corresponding surface immunoglobins. Magnification x440 at 35 mm size. Microcosmos P.39 fig. 2.46