The bovine lymphoid system: II. Derivation and partial characterization of monoclonal antibodies against bovine peripheral blood lymphocytes

An evaluation of the mononuclear cells derived from bovine mammary gland dry secretions using leukocyte antigen specific monoclonal antibodies, light scattering properties and non-specific esterase staining

The distribution of mononuclear cells isolated from the bovine mammary gland during the nonlactating (dry) period was examined using monoclonal antibodies against leukocyte cell surface antigens, cellular light scattering properties, and the presence of nonspecific esterase. Most of the mononuclear cells isolated during the dry period were lymphocytes. T cells predominated until about 1 week prior to parturition. During the week prior to calving, the percentage of B cells increased until it approximated T cells. The ratio of CD4:CD8 cells was 2-3:1 for mammary gland T cells. This was similar to the ratio found in peripheral blood. At dry-off, about 12% of mammary mononuclear cells were macrophages. The macrophage percentage increased (to about 30%) at mid-dry and remained at this levels until parturition. PMN's were isolated with the mononuclear cells during the first 2 weeks dry and the week prior to calving. Three methods were used to identify mammary macrophages. Esterase staining (as an enzymatic method), forward angle/90 degrees light scatter (based on size and internal complexity), and MHC class II/forward angle light scatter (based on size and surface markers) were compared. Each method yielded similar specificity for macrophage identification. Non-adherent cell fractions, obtained by passage of the cells over Sephadex G-10 columns, were enriched in CD4 positive T cells, somewhat depleted of B cells, and depleted of macrophages and PMN's. Cells eluted from G-10 columns, with lidocaine, were mostly lymphocytes, but reflected the cells loaded onto the column.

Detection of B and T cells, with lectins or antibodies, in healthy and bovine leukemia virus-infected cattle

Lectins, polyclonal antibodies and monoclonal antibodies (MAbs) were evaluated as markers for bovine lymphocytes obtained from healthy animals and from cattle infected with bovine leukemia virus (BLV). In the blood from healthy cattle the proportion of cells identified as T lymphocytes with the lectin Helix pomatia (HP) (67.8 +/- 6.2%) using the indirect immunofluorescence technique was similar to the proportion of cells identified by the MAbs P5 (66.1 +/- 3.8%) and BLT-1 (59.8 +/- 7.1%). The proportion of B cells in blood from healthy animals identified with a polyclonal antibody to bovine IgM (18.0%) was similar to that identified with a MAb to bovine IgM (16.2%). However, greater variation between individual values was detected with the MAb (SD = 8.2) than with the polyclonal antibody (SD = 4.0). In the blood from BLV-infected cattle with persistent lymphocytosis, both the polyclonal and the MAb revealed a threefold increase of B cells. A proportion of the B cells had an increased amount of immunoglobulin molecules in their plasma membrane as indicated by flow cytometry. The proportion of T lymphocytes, identified by the MAb P5, was reduced to one-third of that in non-infected cattle. The indirect HP labelling gave inconsistent results and seems not to detect solely T lymphocytes among blood lymphocytes from BLV-infected cattle.

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

Two monoclonal antibodies (MoAbs; BLMo-4 and BLMo-10) were prepared by immunizing with a cell line established from peripheral blood mononuclear cells (PBMC) of enzootic bovine leukosis (EBL) cattle. The specificities of these MoAbs were assayed using bovine PBMC. BLMo-4 reacted with all surface immunoglobulin-positive cells (SIg+ cells; B lymphocytes) and also recognized monocytes, but did not react with T lymphocytes. BLMo-10 recognized a majority, although not all, B lymphocytes, but did not react with either T lymphocytes or monocytes. The antigens recognized by BLMo-4 and BLMo-10 were not Ig, Fc or C3 receptors on the surface of B lymphocytes. The reactivity of the MoAbs with mononuclear cells from the lymphoid organs of adult cattle was studied. BLMo-4 and BLMo-10 did not react with any bone marrow cells. BLMo-10 reacted with 7.4% of thymocytes, and stained the medulla of the thymus in the immunoperoxidase assay. In the case of PBMC, spleen and lymph node cells, the percentage of cells positive for BLMo-4 was slightly higher than that of SIg+ cells, but BLMo-10 showed a slightly lower value.

Monoclonal antibodies that distinguish bovine T and B lymphocytes

The specificities of three monoclonal antibodies (MAbs) were investigated using microcytotoxicity, fluorescence microscopy and laser flow cytometry (LFC) techniques. By microcytotoxicity, bovine thymocytes (n = 4) were estimated to be 85% B26A+, 4% TH21A+, and 1% H4+. Nylon wool enriched peripheral blood T lymphocytes (n = 3) were 90% B26A+, 10% TH21A+ and 10% H4+. Adherent B cell enriched fractions (n = 3) were 10% B26A+, 90% TH21A+ and 90% H4+. The two fluorochrome method was used to simultaneously identify lymphocytes that were sIg+ and MAb+. In these experiments, 92% of all sIg+ cells were H4+. An identical result was obtained for TH21A. 85% of all sIg- cells were B26A+. Using LFC, the mean percentages of sIg+, H4+ and TH21A+ PBL (n = 5) were not significantly different. B26A recognized a significantly greater population of cells, equivalent to the expected percentage of T lymphocytes. LFC also revealed two relatively discrete sizes of B26A+ PBL. The larger population overlapped the size range in which sIg+, H4+, TH21A+ PBL were found. The more numerous smaller B26A+ PBL were in a size range in which few sIg+, H4+ and TH21A+ PBL were found. In a study of MAb reactions with PBL of 185 cows, it was shown that in 92% of the animals H4 and TH21A were positively correlated (r = +.93), when H4 and TH21A were negatively correlated with B26A (r = -.94 and r = -.92, respectively). These correlation coefficients indicate a converse relationship between B26A and both H4 and TH21A. The remaining 8% of the animals were heterogeneous in their expression of the H4 and TH21A markers but not the B26A marker. These results provide strong evidence that: 1) B26A is a pan-T lymphocyte MAb in cattle, 2) a small but significant degree of heterogeneity exists in the expression of the epitopes recognized by H4 and TH21A. However, both MAbs recognize all B lymphocytes of most individuals, and 3) using a variety of immunological methods these three MAbs can now reliably be used to assay bovine T and B lymphocytes.

Production of monoclonal antibodies to bovine leukocyte cell-surface components

Fusion of murine myeloma cells with syngeneic spleen lymphocytes has led to development of hybridomas secreting antibodies. Hybrid cells retain the immortality and clonability of myeloma parents as well as the antibody-producing property of lymphocytes. Specificity of monoclonal antibody produced is based on the one lymphocyte-one antibody phenomenon and represents the most effective process for producing specific antisera. spleen cells from mice immunized with desired antigen are hybridized with nonsecreting mouse myeloma cells. Resulting hybrids are cloned and culture fluids tested for specific antibody activity to the antigen. Positive clones are cultivated in vitro and injected into mice for monoclonal antibody production. This technology has been extended to the bovine species to obtain monoclonal antisera to immunoglobulins and cell-surface components of leukocytes for study of mammary gland immunity. Recent progress in monoclonal research has led to interspecific fusion of murine myelomas with bovine lymphocytes, resulting in hybridomas that produce monoclonal bovine immunoglobulins. Monoclonal antibodies will be useful in investigations applicable to bovine research including purification of immunoglobulins, determining immunoglobulin concentration in colostrum and milk, reference reagents for bovine serology, antibody localization in tissue, gene sequencing, characterizing histocompatibility antigens, distinguishing and quantitating cell types in blood, milk, and udder tissue, and elucidating role of cell subpopulations in the immune response.

Evaluation of labelling methods for bovine T and B lymphocytes

Two lectins, one from Helix pomatia (HP) and one from Peanut (PN), were evaluated as bovine T cell markers. HP attaches to about 40% of the bovine peripheral blood lymphocytes (PBL). With an indirect technique about 60% of PBL are HP positive, while PN attaches to a slightly higher proportion of the PBL. In double labelling experiments, HP was shown to bind only to Ig negative cells while 2% of the PBL were double labelled with PN and anti-Ig. The influence of different pretreatments of the PBL or the antibodies for labelling of the membrane bound Ig was studied. Preincubation for detaching cytophilic antibodies was important to avoid false Ig positive cells.

Lymphocyte markers in the bovine foetus

The ontogeny of lymphocyte surface markers was studied in thymus, retropharyngeal lymph nodes, spleen, bone marrow, and liver of 48 bovine foetuses, 80-280 days of gestation. The markers examined were the spontaneous (E) rosette against sheep erythrocytes (SRBCs) in foetal calf serum (E/FCS), in medium supplemented with gelatin (E/CFG), and in medium supplemented with dextran (E/dextran), the erythrocyte-antibody (EA) rosette for immunoglobulin (Fc) receptors, the erythrocyte-antibody-complement (EAC) rosette for complement receptors, and the immunofluorescence test (IFT) for surface-membrane immunoglobulins (SmIg). E-rosette-forming cells (RFCs) occurred in the thymus in substantial numbers throughout the period studied, in spleen and lymph nodes only after 160 days, and in bone marrow and liver rarely. The dynamics of E rosettes formed in the three supplements suggested that each supplement might be supporting rosette formation by different populations of cells, albeit considerable overlap might be expected. Organ distribution and development of EA and EAC RFCs did not parallel the expected ontogeny of any class of lymphocytes. Cells carrying SmIg developed mainly in spleen and lymph nodes. Towards the end of gestation some cells in liver also had SmIg.

Hybridomas: a new dimension in biological analyses

Since the first report of hybridomas producing monoclonal antibodies by Kohler and Milstein in 1975, this technique has spread to nearly all areas of biological, biochemical, and biomedical research. Watching the use of these methods spread from immunologists to cell biologists, developmental biologists, biochemists and to other biological disciplines and observing the nearly logarithmic increase in publications using these reagents has been in itself fascinating and informative. An overview of the development of this technology and its applications is presented including the use of monoclonal antibodies to study cell surface molecules, differentiation antigens, receptors, and histocompatibility antigens. The use of these antibodies to analyze microorganisms and parasitic antigens as well as their use in the genetic analysis of human cell surface antigens and the detection of polymorphic variation in enzymes and other proteins is discussed. Examples of the application of monoclonal reagents to the study of tumor cell biology including the labeling of metastatic tumor cells and the detection of cell surface molecules implicated in the regulation of growth control and cell division are provided.