the invention is explained in more detail below with the aid of application examples and implementation examples . preparing and characterizing monoclonal antibodies which are directed against the cell surface glycoprotein sirp recombinant fusion proteins which contain the entire extracellular domain of sirpα1 ( sirpα1ex ) or sirpβ1 ( sirpβ1ex ) are used as antigens . the sequence of the extracellular domain employed is depicted in the two abovementioned publications . four to eight week - old female balb / c mice are immunized three times , at intervals of 14 days , with 15 μg of protein which has been diluted 1 : 2 in ribi adjuvant ( pansystems , aidenbach , germany ). four days after the last injection , the spleen was removed and fused with myeloma cells of the known strain sp2 / 0 . the fused cells were cultured and the specific antibodies were then selected on a cell line which had been transfected with sirpα1 or sirpβ1 . methods which are well known in skilled person circles were used to produce , purify and characterize the antibodies . the reactivities and properties of the various sirp antibodies which were prepared in this way can be taken from the attached table and the following examples . n . b . = no binding of cells to sirpβ1ex with any of the haematopoietic cells which have so far been tested monoclonal antibodies b1d5 and b4b6 are specific for sirpβ1 . all the sirpα1 - specific monoclonal antibodies also react with sirpβ1 , which means that the antibodies se5a5 , se7c2 , se12b6 and p3c4 can be regarded as being specific for sirp since other members of the sirp family possess very similar extracellular domains . the monoclonal antibody p3c4 was used to investigate the surface expression of sirp on mononuclear bone marrow cells and peripheral blood cells . by means of immunofluorescence , it was possible to demonstrate that the strongest expression is present on monocytes while there is moderate expression on granulocytes and virtually no expression on lymphocytes . cd83 + dendritic cells were likewise strongly positive with regard to sirp . an investigation of the coexpression of cd antigens and sirp on various bone marrow cells showed that sirp was expressed most strongly on c33 + and cd34 + myeloid / monocytic precursor cells . in addition to this , sirp is also expressed on cd19 + b lymphoid cells and on immature cd117 + and ac133 + precursor cells . by contrast , no expression of sirp was found on cd3 + t cells , cd56 + natural killer cells or glycophorin a + erythroid precursor cells . it follows from this that , in bone marrow , sirp is essentially found to be expressed on myeloid and cd34 + stem cells and precursor cells . in order to further analyse the sirp + subsets , cd34 + bone marrow cells were purified by means of macs and stained with antibodies directed against cd34 , sirp and selected cd markers . it was found that sirp is expressed on cd34 + cd90 + , cd34 + cd117 + and cd34 + cd164 brigt stem cells and myeloid subsets but not on cd34 + cd19 + b cell subsets or cd34 + cd71 brigt erythroid precursor cells , suggesting that sirp plays a role in the regulation of stem cell growth and differentiation . the above results can be interpreted to the effect that sirp is not only involved in the function of myeloid cells but also plays an important role in the regulation of stem cell differentiation . the antibody p3c4 was likewise employed to examine , by means of immunofluorescence , the expression of sirp on acute myeloid leukaemia ( aml ) blasts and on chronic myeloid leukaemia ( cml ) blasts . it was found that , in contrast to normal myeloid cells , all four of the myeloid cml blast populations analysed , and 26 out of the 59 aml blast populations which were tested , were sirp − , while 15 out of the 59 aml blasts expressed sirp to a small degree and only 18 out of the 59 blasts expressed sirp to the same degree as do normal myeloid or monocytic cells in bone marrow . all the immature leukaemic blasts of the m0 or m1 fab type were sirp − or expressed sirp to a small extent . these results provide evidence that sirp expression is downregulated on many leukaemic blasts . on the basis of the above results , it is possible that the reduced expression of sirp in most leukaemic blasts is either the cause or a consequence of the defective proliferation of these cells . in order to investigate the possible interaction of sirp with cellular components on normal and malignant haematopoietic cells , cell binding tests were carried out using immobilized fusion proteins of sirpα1ex , sirpα2ex and sirpβ1ex . all the myeloblast , monoblast , erythroblast , megakaryoblast , and b lymphoblast and t lymphoblast cell lines which were tested bound strongly to sirpα1ex and sirpα2ex but not to sirpβ1ex , with dilution series demonstrating that b lymphoblast and t lymphoblast cell lines possess a larger number of binding sites for sirp . it was furthermore possible to demonstrate that some of the monoclonal antibodies according to the invention inhibit the binding of cells to sirpα1ex and sirpα2ex , as is shown in the table from example 1 . further investigations of the expression of possible sirp ligands showed that soluble sirpα1ex and sirpα2ex bound strongly to lymphocytes , while their binding to monocytes and granulocytes was substantially weaker . in order to identify the extracellular ligand for sirpα1 and sirpα2 on haematopoietic cells , the sirp - negative , but strongly sirpα1ex - binding and sirpα2ex - binding , ccrf - cem cells were used to produce monoclonal antibodies which inhibit the binding of sirpα1ex and sirpα2ex to these cells . the antibody cc2c6 , which was found in this context , blocked this binding completely . the cellular reactivity of this antibody was compared with that of 166 different antibodies directed against cd molecules , in connection with which it emerged that cc2c6 recognizes cd47 as being the extracellular ligand for sirpα1 and sirpα2 . it was furthermore found that only functionally active , cd47 - specific monoclonal antibodies are able to block the interaction between cd47 and sirp completely , while non - functional monoclonal antibodies have no effect on this interaction . this suggests that the binding of sirp to cd47 is essential for many of the functions described for cd47 . in the light of this , both the blocking and the non - blocking antibodies according to the invention are valuable tools for investigating the participation of sirp in various immunological processes in vitro .
monoclonal antibodies which bind specifically to the extracellular domain of the sirp cell surface glycoproteins , and which , in some cases , block the interaction of sirp with the surface molecule cd47 , are described .