Preparation and characterization of monoclonal antibodies against bovine B lymphocyte surface antigens

Analysis of bovine B cell reactive monoclonal antibodies

Monoclonal antibodies (mAbs) submitted to the workshop B cell panel were screened for reactivity with bovine surface immunoglobulin positive (SIg+) cells from tonsil, mesenteric lymph nodes (MLN), ileal Peyer's patches (IPP), thymus and peripheral blood by fluorescence activated cell sorter (FACS) analysis. All mAbs within B cell panel reacted with B cells except the negative control mAb VPM61. Although most mAbs stained the majority of B cells from different tissues, 14 mAbs did not stain B cells from IPP. Detailed FACS analysis of the 24 mAbs in preliminary clusters PC17, PC28, PC29, PC30, PC35, PC41 and PC43 showed all preliminary clusters (PC) to contain mAbs with similar and variable specificities. This absence of clear-cut clusters therefore did not permit a simple classification of B cell surface antigens via the B cell mAbs and suggests considerable complexity and variability of the B cell surface.

Identification of bovine B cell reactive and B cell specific monoclonal antibodies

All monoclonal antibodies (mAbs) submitted to the workshop panel were screened for reactivity with bovine surface immunoglobulin (sIg)+ cells (gated small dense lymphocytes from peripheral blood) by fluorescence activated cell sorter (FACS) analysis. Eighteen temporary clusters--TCs 1-12, 15, 16, 18, 19, 25 and 26--contained mAbs reactive with sIg+ cells. mAb BAS21A (unclustered) and CC92 (TC25) were also reactive with sIg+ cells. Further FACS analysis with B cells from peripheral blood lymphocytes and mesenteric lymph nodes, and B and T lymphoma cell lines, indicated that the majority of mAbs within TCs 2, 4, 15, 18 and 26 reacted specifically with bovine B cells. Bovine B cell specific mAbs within these clusters were TH14B, IL-A55, CACT101A, MUC76A from TC4, VPM30, GC65A, CACT65A from TC15, IL-A58, CC56, CC70, IL-A65 from TC18, and CC57 and 26A9 from TC26. Three mAbs--IL-A65, CC70, and BAQ15A--within TC18 defined WC3; mAbs TD9 and CC56 may also be related to WC3.

Properties of nine continuous B-cell lines established from enzootic bovine leukosis tumors

We established 9 cell lines from 63 tumor cases of enzootic bovine leukosis and studied their properties. Cells of all lines formed small clumps and floated in culture medium, indicating growth. Four of the 9 cell lines were surface immunoglobulin (SIg)-positive, but the remaining 5 line cells were negative for SIg or, if SIg was detected, the percentage of SIg-positive cells was very low. Tests for the properties of the cells with monoclonal antibodies to lymphocytes revealed that the established line cells are B-lymphocytes. Morphological observation also revealed that they had the morphology of B-lymphoblastic cell. The results of E and EAC rosette assay were negative, but 6 of 8 cell lines were positive for EA rosetting. All the 9 cell lines reacted with MoAb C-143, which recognizes the tumor-associated antigen (TAA) of the EBL tumor cell. All 9 cell lines produced bovine leukosis virus (BLV). These results suggest that the 9 cell lines are tumor cells derived from B-lymphocytes of EBL.

FACS analysis of bovine leukemia virus (BLV)-infected cell lines with monoclonal antibodies (mAbs) to B cells and to monocytes/macrophages

The eighteen monoclonal antibodies (mAbs) to B cells and the fourteen mAbs to accessory cells submitted to the workshop were analysed by FACS on three established, bovine leukemia virus (BLV)-infected bovine cell lines. Several mAbs of previously defined specificity were run in parallel. This analysis allowed us to gain further insight on the precise phenotype of those peculiar cells and to cluster the submitted mAbs according to their staining patterns. The BLV-infected cell lines seemed to belong to the B cell type though some of them lack detectable surface immunoglobulins. Moreover, all lines express the CD5 T cell marker and several myeloid markers.

Characterization of monoclonal antibodies to channel catfish, Ictalurus punctatus, leucocytes

Four monoclonal antibodies (MAbs) were evaluated for specific reactions to various catfish peripheral blood leucocytes and anterior kidney cells. The MAb 9E1 served as a standard and positive control for all test reactions because of its defined reactivity with channel catfish immunoglobulin and immunoglobulin bearing cells. Of the four MAbs, two have been characterized as being specific for a non-immunoglobulin marker on lymphocytes, thus marking T lymphocytes and two were specific for catfish neutrophils. Morphological, flow cytometric and functional analysis of the reactive cells verified these findings.

A monoclonal antibody specific for bovine T cell surface antigen associated with the E-rosette receptor

From mice immunized with T lymphocyte-enriched bovine peripheral blood mononuclear cells (PBMC), a monoclonal antibody termed BLMo-12 was obtained. BLMo-12 reacted with the antigen of Mr 56,000 in lysate of T lymphocytes. This mAb was found to inhibit spontaneous rosette formation by T-bovine lymphocytes with sheep red blood cells but it did not react with B lymphocytes, monocytes, neutrophils or eosinophils. In frozen section of the thymus, BLMo-12 showed a positive staining both the cortex and the medulla. In lymph nodes, the mAb stained the T-dependent paracortex. BLMo-12 reacted with 49.9% of PBMC and 82.5% of thymocytes. Recognition of the bovine homologue of CD2 on the T lymphocyte surface by this mAb was discussed.

Negative enrichment of bovine T lymphocytes with monoclonal antibodies and magnetic microspheres

A highly enriched population of bovine T lymphocytes was produced from peripheral blood leukocytes following the depletion of monoclonal antibody-labelled B lymphocytes and monocytes with magnetic microspheres. This negative-enrichment protocol was simple, rapid, and specific. Also, it had a high recovery efficiency and was consistently reproducible. The enriched T lymphocytes proliferated in response to recombinant bovine interleukin 2 and, following the addition of monocytes, to concanavalin A. This methodology made it possible to determine the proliferative responses of peripheral blood lymphocytes utilizing a constant number of T lymphocytes within each assay. In this way, the in vitro T lymphocyte responses were determined independent of changes in the number of responder cells within peripheral blood.

Spontaneous regression of bovine cutaneous leukosis

Biopsies of skin from a 2-year-old heifer with spontaneously regressing dermal leukosis were examined. The heifer was not infected with bovine leukemia virus and was negative for tumor-associated antigens of enzootic bovine lymphosarcoma. By hematological standards for bovine leukemia, the heifer was positive at about 60 days post-occurrence of the disease (POD). At 53 days POD, lymphoblastic neoplastic cells in the dermis reacted with anti-T lymphocyte monoclonal antibody by the avidin biotin peroxidase complex method. The cells had intracytoplasmic clustered dense bodies under electron microscopy. From 53 to 83 days POD, figures of the transepithelial elimination (TE) against neoplastic cells and perivascular infiltration of small lymphocytes were in the dermis. Small lymphocytes reacted with anti-T lymphocyte monoclonal antibody. At necropsy there were no neoplastic lesions; there were flat lymph node-like tissues in the subcutis. Many germinal centers were seen in the lymphatic organs. Blood lymphocytes at 46 days POD were stimulated by phytohemagglutinin-P and concanavalin A. Sera, taken until 75 days POD and at necropsy, showed an inhibitory effect on mitogen-induced blastogenesis of normal bovine lymphocytes. These results suggested the existence of a spontaneous regressive mechanism against neoplastic lesions by TE and tumor immunity.