Characterization of lymphocyte subpopulations in sheep by rosette formation, adherence to nylon wool and mitogen responsiveness

γδ T cells in artiodactyls: Focus on swine

Vaccination is the most effective medical strategy for disease prevention but there is a need to improve livestock vaccine efficacy. Understanding the structure of the immune system of swine, which are considered a γδ T cell "high" species, and thus, particularly how to engage their γδ T cells for immune responses, may allow for development of vaccine optimization strategies. The propensity of γδ T cells to home to specific tissues, secrete pro-inflammatory and regulatory cytokines, exhibit memory or recall responses and even function as antigen-presenting cells for αβ T cells supports the concept that they have enormous potential for priming by next generation vaccine constructs to contribute to protective immunity. γδ T cells exhibit several innate-like antigen recognition properties including the ability to recognize antigen in the absence of presentation via major histocompatibility complex (MHC) molecules enabling γδ T cells to recognize an array of peptides but also non-peptide antigens in a T cell receptor-dependent manner. γδ T cell subpopulations in ruminants and swine can be distinguished based on differential expression of the hybrid co-receptor and pattern recognition receptors (PRR) known as workshop cluster 1 (WC1). Expression of various PRR and other innate-like immune receptors diversifies the antigen recognition potential of γδ T cells. Finally, γδ T cells in livestock are potent producers of critical master regulator cytokines such as interferon (IFN)-γ and interleukin (IL)-17, whose production orchestrates downstream cytokine and chemokine production by other cells, thereby shaping the immune response as a whole. Our knowledge of the biology, receptor expression and response to infectious diseases by swine γδ T cells is reviewed here.

Sepracell-MN for mononuclear cell separation from cattle: effect on mitogen-and antigen-induced lymphocyte blastogenesis

Mononuclear leukocytes (MNC) were separated from heparinized and EDTA-treated whole bovine blood by centrifugation after mixing with a commercial colloidal silica preparation (Sepracell-MN (S-MN]. Cell yields and lymphocyte blast transformation (LBT) to pokeweed mitogen (PWM), phytohaemagglutinin (PHA), concanavalin A (Con A), and Brucella abortus antigens were tested against MNC obtained from heparinized whole blood using Ficoll-Hypaque (FH). Separation with S-MN was more rapid and less labor intensive than separation with FH. There was a higher average total yield of MNC but a lower percentage of monocytes in the FH- than in the S-MN-separated MNC. In mitogen-induced LBT assays, MNC responded comparably to each mitogen regardless of the separation technique or anticoagulant used, and a cell concentration effect was demonstrated. In general, FH-separated MNC responded greater to PWM than did S-MN/EDTA separated MNC, but S-MN/heparin separated MNC had the greatest LBT responses to PWM. Overall, S-MN/EDTA separated MNC had the greatest responses to PHA, and responses to Con A were variable among experiments with respect to the separation technique. In antigen-induced LBT assays, two B. abortus antigens were used: a heat-killed strain S1119 (HKA) and a gamma-irradiated strain 19 (gamma BA). The LBT responses of three steers vaccinated with live B. abortus strain 19 were compared with three nonvaccinated steers in three separate experiments. Using HKA, FH separation resulted in an overall greater LBT response for vaccinates than nonvaccinates and a greater differential between responses of vaccinates and nonvaccinates than did S-MN derived MNC regardless of the anticoagulant used. Using gamma BA, FH produced the most responsive MNC in one experiment and S-MN/heparin produced the most responsive MNC in the other. At the highest cell concentration tested, FH-separated MNC had the greatest LBT responses for vaccinated calves, but differences between S-MN- and FH-separated MNC responses were not significantly different (P greater than 0.05). In conclusion, S-MN is a rapid and simple technique for separation of MNC from bovine blood. The technique produces an adequate cell population for mitogen-induced LBT studies; however, FH-separated MNC were generally more responsive in the B. abortus-induced LBT assay.

Lymphocyte subpopulations in sheep during the early stage of experimental infection with bovine leukaemia virus

Sheep were experimentally infected with bovine leukaemia virus (BLV) by the inoculation of PBL from leukaemic sheep. Antibodies to viral structural proteins were detected at from 2 to 6 weeks after inoculation. At seroconversion, all sheep had a marked increase in the number of circulating lymphocytes, due essentially to an increase in the number of B cells. The number of circulating B cells then decreased but remained higher than pre-infection levels. A second increase in this population preceded the development of a B cell lymphoblastic leukaemia. Generalized lymphosarcoma was diagnosed at necropsy of all sheep. Variation between individual sheep in the time from infection to the development of tumours allowed two clearly delineated groups of nine sheep to be compared. A study of changes in the B cell and T cell populations during the first 16 weeks of infection suggested that the initial response to infection influences the subsequent rate of leukaemogenesis. At seroconversion the number of circulating B cells was significantly higher in group 1 (10.16 +/- 1.51 X 10(9)/l) than in group 2 (6.47 +/- 2.76 X 10(9)/l). Group 1 sheep became leukaemic at 20-50 weeks after infection, whereas group 2 sheep did not do so until 70-95 weeks after infection.

The use of fluorescent probes as markers for sheep lymphocyte subpopulations

Sheep blood lymphocytes were labelled with fluorescent probes and examined under the fluorescence microscope and by the fluorescence-activated cell sorter. A novel probe using fluorescamine, coupled to hexylamine, detected 22.9% of cells, apparently of the B-cell series, counted by fluorescence microscopy. Substitution of fluorescein isothiocyanate (FITC) for the fluorescamine did not label the same subpopulation of cells although the lymphocytes could then be examined in the cell sorter. A larger number of cells (38.8%) formed the brighter cluster but did not behave as B cell when separated on nylon-wool columns. Improvement in discrimination of the cell populations was obtained with FITC-hexadecylamine (C16). This probe detected 38% of cells in the smallest cluster, 44% of cells in the intermediate cluster and 19% of cells in the brightest cluster. The proportion of cells in each cluster appeared to parallel closely the "null", erythrocyte (E) rosette-forming T cells and the B cells detected by conventional markers for blood lymphocytes. Other fluorescent probes, formed from FITC and other amines and amino acids, labelled lymphocyte membranes. Probes with a terminal charge labelled the small cluster particularly well, whereas those that were terminally non-polar labelled the larger cells brigthly, but not to the same intensity as the charged probes in the small cells.

Importance of the hour of sampling in the lymphoblastic transformation assay of sheep peripheral blood lymphocytes

This paper describes the effect of the nycthemeral cycle on the lymphocyte response of sheep to different mitogens (PHA, Con A and PWM). A considerable decline in the lymphocyte response was evident in the afternoon and early in the morning in all 6 animals tested. Three peak responses were identified during a 24 hour study period, at 14.00 h, 24.00 h and 08.00 h. The results presented here suggest that this variation in lymphocyte response is a meaningful difference in the response ability of individual lymphocytes. Factors affecting the number of leukocytes and the proportion of different types of lymphocytes in peripheral blood might be the essential causes of variation. To obtain an accurate indication of an individual's immunocompetence, it is important to make a preliminary determination of the optimal hour for sampling. If this is not possible, all the samples must be taken at the same hour on each test day, in order to make significant comparisons.

Blastogenic response of peripheral blood lymphocytes from multiparous pregnant ewes

The immunocompetence of pregnant multiparous ewes was investigated with respect to the blastogenic response of peripheral blood lymphocytes of (PBL) to three mitogens: PHA, Con A, and PWM. The profile of PBL responses shows 1) progressive suppression at 36 and 66 days of gestation, 2) enhanced response at 97 days of gestation, which approaches the mean values observed at the premating period, and 3) a redecline of the response at 137 days of gestation to depressed values lower than observed at 36 and 66 days of gestation. The results suggest that mitogen-treated lymphocytes were depressed and that the immunodepressive factor(s), which can influence lymphocytes at the systemic level, may be involved in the maintenance of the ovine fetal semiallograft.

[Lymphocyte markers in domestic animals. I. Mitogenic lectins and non-mitogenic lectins]

The authors reviewed the lymphocyte markers in domestic animals. The first part is devoted to lectins. The general and methodologic aspects of lectins as mitogens are studied. The main mitogen lectins are emphasized in regard to their field of utilisation and the technical aspect of their use. The non-mitogen lectins are presented for cell suspension or tissue section staining.

Suppression of antigen- and mitogen-induced proliferation of bovine lymphocytes by excretory-secretory products of Oesophagostomum radiatum

Excretory-secretory products (ESP) isolated from in vitro-grown stage-3 to -4 larvae of Oesophagostomum radiatum were found to inhibit both the in vitro antigen-specific proliferation of keyhole limpet hemocyanin- and ovalbumin-primed lymphocytes and the proliferation induced by the T-cell mitogen concanavalin A. As little as 50 ng of ESP protein per culture resulted in 50% reductions of subsequent proliferative responses. Antigen-induced responses were 100 to 1,000 times more sensitive to inhibition than were mitogen-induced responses. The inhibitory activity was found to affect the induction of proliferation as evidenced by the observation that complete inhibition was seen when ESP were added to cultures within the first 24 h. ESP were found to have no inhibitory activity when added 72 h after the initiation of the cultures. The inhibition was not a result of a direct action upon macrophages because pulsing of adherent cells with ESP had no more effect on a subsequent proliferative response than did a pulsing of the culture vessel itself. The inhibitory activity eluted from high-pressure liquid chromatography columns in the same fractions as protein standards with molecular weights of 25,000 to 35,000. Of special interest is the fact that this inhibitor of the expansion of immunoreactive clones of lymphocytes is found associated with the stages of parasites most intimately associated with host tissues, namely larval stages 3 and 4.

A method of purifying sheep sIg+ lymphocytes as a tool for class II MHC antigen analysis

A method is described for the purification of sheep lymphocytes carrying class II MHC antigens. After incubation of purified blood lymphocytes on anti-IgM-coated petri dishes, the adherent fraction contained 95% sIg-positive cells determined by immunofluorescence. When tested with cross-reacting anti-class II (bovine and human) monoclonal antibodies, more than 95% of these cells were positive either by immunofluorescence or cytotoxicity. This technique will permit studies of the polymorphism of sheep class II antigens.

Lymphoblastic transformation assay of sheep peripheral blood lymphocytes: a new rapid and easy-to-read technique

A new micro-method was used to evaluate in vitro sensitivity of ovine peripheral blood lymphocytes (PBL) to different non specific mitogens (pHA, Con A, PWM) and to investigate the interest of a colorimetric assay for measurement of transformed lymphocytes. The results showed that sheep PBL in flat-bottomed microplates responded optimally at a cell density of 8 X 10(6) cells/ml to PHA (2.5 micrograms/ml), Con A (5 micrograms/ml) and PWM (5 micrograms/ml). The colorimetric assay using a tetrazolium salt (MTT), for measuring the transformed lymphocytes, is very well correlated with the classical method of [3H]thymidine incorporation. This new revelation technique of the mitogenic response improve the technical value of the assay, which is more rapid and easy-to-read, without diminishing the biological value.

Nylon wool column fractionation and characterisation of feline lymphocyte subpopulations

Feline separated mononuclear cells (SMC) were obtained from peripheral blood by ficoll-diatrizoate gradient separation. SMC were further fractionated on nylon wool columns into nylon wool adherent cells (NWAC) and nylon wool effluent cells (NWEC). The three cell populations, SMC, NWAC and NWEC, were characterised using direct immunofluorescent staining for surface immunoglobulin (sIg) as a B cell marker and neuramidase treated guinea pig erythrocyte-rosette formation (E-rosettes) and mitogen-induced lymphocyte blastogenesis (LB) as possible T-cell markers. Feline SMC consisted of 30.1 +/- 4.0% sIg+ cells 36.6 + 5.4% E-rosette forming cells and 33.3% null cells i.e. cells which were sIg- and non E-rosette forming. Fractionation of SMC on nylon wool columns yielded NWEC which were significantly enriched for T cells in that they contained 68.6 +/- 2.9% E-rosette forming. Fractionation of SMC on nylon wool columns yielded NWEC which were significantly enriched for T cells in that they contained 68.6 +/- 2.9% E-rosette forming cells. NWAC were 51.0% +/- 10.8% sIg+, approximately 20% of cells were lost. The LB responsiveness of NWEC to concanavalin A (Con A) and phytonaemagglutinin-P (PHA-P) was enhanced compared to SMC. NWAC were non-responsive to Con A and PHA-P at all concentrations tested. It was concluded that nylon wool column fractionation of feline SMC was an efficient procedure for T cell enrichment and that the enriched cells retained the properties of E-rosette formation and blastogenesis by mitogens.

An immunological classification of ovine lymphomas

Sporadic ovine lymphoma cells were identified as T or B lymphocytes with a T cell-specific antiserum or by detecting surface immunoglobulin. Lymphomas were classified as being of T or B cell origin if 60 per cent, or more, of the cells were of the respective type. Of 16 lymphomas, 6 were T cell and 6 were B cell derived. In one lymphoma more than 60 per cent of the cells were identified as both T and B cells. In the other 3 lymphomas neither T nor B cells reached this value; 2 of these had negligible T and B cell numbers and were classified as null cell lymphomas. A relationship was seen between the immunological and anatomical classifications of the lymphomas in that all the T cell lymphomas were of multicentric distribution while 4 of the 6 B cell neoplasms were confined to the alimentary tract and its associated lymphoid tissue. In contrast, there was no relationship between the immunological and histological classifications of the lymphomas.

A major subpopulation of Fc receptor-bearing lymphocytes revealed by rosette formation in dextran media: studies with pig, sheep and rat lymphocytes

Blood lymphocytes from young pigs which formed 9.1 +/-0.7% Fc rosettes (mean +/- S.E., range 4.1-16.0), with rabbit and pig immunoglobulin-coated indicator cells used in optimum conditions in phosphate-buffered saline (PBS), formed 32.6 +/- 1.8% (16.9-44.3) in the presence of 4% dextran (DFc). The proportion of DFc+/Fc+ lymphocytes varied from 2.2 to 5.9 (3.8 +/- 0.3). Compared with the PBS test, in dextran rosettes are formed with more lymphocytes and with red cells coated with less immunoglobulin. Ficoll at 14% gave similar enhancement. Dextran enhancement of Fc rosettes was also observed with sheep PBL, but not with rat thoracic duct lymphocytes. The FC portion of IgG is responsible for both Fc and DFc rosettes. Thus most Fc and DFc rosettes, formed with serum antibody-coated bovine RBC, are revealed by IgG coated but not F(ab')2-coated BRBC, and show dose-dependent inhibition in the presence of free pig IgG (complete at 5-10 mg/nl) but not IgM (up to 2 mg/ml). Separation of lymphocytes on nylon wool suggests that DFc rosettes are formed by B cells and some T cells. Over half of the weak Fc rosette-forming lymphocytes (DFc-Fc) elute in the non-adherent fraction, which contains few B cells, and therefore are a subpopulation of T cells.