Definition: In this task, you're given a paragraph from the research paper and your task is to generate a suitable title for the research paper based on the given paper. Under 100 words is a good title length.
Input: We isolated a replication-competent, neurotropic retrovirus (FrC6 virus) and its molecular clone A8 from the NB-tropic Friend murine leukemia virus (FLV) complex. For detection and characterization of the FrC6 and A8 viruses, monoclonal antibodies (MAbs) against the FLV complex were established. Thirty MAbs, each of which reacted with the FLV-producing cell line, were tested for potential neutralizing activities; only two MAbs inhibited the proliferation of the A8 virus. These two MAbs were ineffective or had very weak neutralizing activities toward the non-neurotropic FLV strain clone 57 virus. Further characterization of MAbs by immunoprecipitation revealed that 4 MAbs recognized the envelope protein of the A8 virus. Two of these 4 MAbs recognized the surface glycoprotein gp70, requiring the conformational epitope of the virus for this recognition, while the other two MAbs, which were reactive with the transmembrane protein pl5E, were conformationindependent. Both of the MAbs against gp70 distinguished neuropathogenic and non-neuropathogenic viruses to some extent, through neutralizing activity or binding activity detected by immunoprecipitation, whereas the two MAbs against pl5E reacted with the viruses in a similar manner. Furthermore, one of the MAbs distinguished the viral antigen in the wall of the vacuolation that composes the spongiotic lesion induced by FrC6 viral infection of the brain. The Friend virus complex, composed of the replication-competent Friend murine leukemia virus (FLV) and the replication-defective spleen focus-forming virus * Corresponding author. Fax: +81 (426) 91 9315. 0168-1702/95/$09.50

Characterization of monoclonal antibodies recognizing neurotropic Friend murine leukemia virus