A method for identifying, selecting and isolating plasma cells and/or plasmablasts that produce antibodies specific for target antigens, comprising: a) mixing lymph fluid, lymphoid tissue, blood cell sample, or bone marrow derived cells with (i) a marker that binds specifically said antibodies wherein the marker is the target antigen itself, or a substance that contains the same epitope, labelled with a fluorescent label or with magnetic beads; and (ii) a marker for plasma cells and/or plasmablasts, wherein the marker is a fluorescent probe that enables identification using fluorescence scanner, fluorescence microscope, flow cytometer or a cell sorter, which fluorescent probe stains selectively the endoplasmic reticulum more than it stains other cell organelles such as plasma-membrane, mitochondria, Golgi body, lysosome, peroxisome, nucleus, centrosome, cytoplasm, phagosome, endosome, or aggresome; b) isolating cells bound by both markers (i) and (ii), which are plasma cells/plasmablasts that bind specifically to the target antigen by using a cell sorter, thereby excluding - cells bound only by marker (i), which are cells that are bound to the target antigen but are not plasma cells/plasmablasts; and - cells bound only by marker (ii), which are plasma cells/plasmablasts but do not bind specifically to the target antigen; wherein the said lymph fluid, lymphoid tissue, blood cell sample, or bone marrow derived cells are - samples collected from a human or non-human animal and subsequently sensitized in vitro with the target antigen; or - samples collected from humans that have antibodies against the target antigen; or - samples collected from non-human animals previously immunized with the target antigen. a) mixing lymph fluid, lymphoid tissue, blood cell sample, or bone marrow derived cells with (i) a marker that binds specifically said antibodies wherein the marker is the target antigen itself, or a substance that contains the same epitope, labelled with a fluorescent label or with magnetic beads; and (ii) a marker for plasma cells and/or plasmablasts, wherein the marker is a fluorescent probe that enables identification using fluorescence scanner, fluorescence microscope, flow cytometer or a cell sorter, which fluorescent probe stains selectively the endoplasmic reticulum more than it stains other cell organelles such as plasma-membrane, mitochondria, Golgi body, lysosome, peroxisome, nucleus, centrosome, cytoplasm, phagosome, endosome, or aggresome; (i) a marker that binds specifically said antibodies wherein the marker is the target antigen itself, or a substance that contains the same epitope, labelled with a fluorescent label or with magnetic beads; and (ii) a marker for plasma cells and/or plasmablasts, wherein the marker is a fluorescent probe that enables identification using fluorescence scanner, fluorescence microscope, flow cytometer or a cell sorter, which fluorescent probe stains selectively the endoplasmic reticulum more than it stains other cell organelles such as plasma-membrane, mitochondria, Golgi body, lysosome, peroxisome, nucleus, centrosome, cytoplasm, phagosome, endosome, or aggresome; b) isolating cells bound by both markers (i) and (ii), which are plasma cells/plasmablasts that bind specifically to the target antigen by using a cell sorter, thereby excluding - cells bound only by marker (i), which are cells that are bound to the target antigen but are not plasma cells/plasmablasts; and - cells bound only by marker (ii), which are plasma cells/plasmablasts but do not bind specifically to the target antigen; - cells bound only by marker (i), which are cells that are bound to the target antigen but are not plasma cells/plasmablasts; and - cells bound only by marker (ii), which are plasma cells/plasmablasts but do not bind specifically to the target antigen; - samples collected from a human or non-human animal and subsequently sensitized in vitro with the target antigen; or - samples collected from humans that have antibodies against the target antigen; or - samples collected from non-human animals previously immunized with the target antigen.