Human recombinant interleukin-2 augments in vitro blastogenesis of bovine and porcine lymphocytes

Compatibility of porcine and human interleukin 2: implications for xenotransplantation

BACKGROUND

Xenotransplantation provides a possible solution to the severe shortage of allogeneic organ donors. The pig, which shares many physiological similarities with humans, makes it an optimal species for preclinical experimentation and clinical applications. Interleukin 2 (IL2) is a potent growth factor secreted primarily by T helper lymphocytes and it is vital to the cellular expansion required for a productive immune response and the development and peripheral expansion of CD4+CD25+ regulatory T cells. Therefore, it is essential to understand of the compatibility of IL2 between pigs and humans.

METHODS

We first compared the cDNA and protein sequences and the crystal structures of human and porcine IL2 and IL2 receptors, respectively. The effect of IL2 to induce T cell proliferation was determined by 3H-thymidine incorporation and cell cycle detection.

RESULTS

Porcine IL2 induced very limited proliferation of human lymphocytes while it functioned well on porcine lymphocytes. Human IL2 had remarkably reduced effects on porcine lymphocytes whereas it worked well on human lymphocytes.

CONCLUSION

Our present study showed that the interaction of IL2 and IL2R across species might have defects. Together with the wide physiological functions of IL2, our data indicated that physiological disorders could be caused by the poor function of xenogeneic donor IL2 on host cells in full hematopoietic chimera. Our data suggested an additional potential advantage for the mixed xenogeneic chimeras.

Expression and characterisation of equine interleukin 2 and interleukin 4

In the present study, we describe the expression of equine IL2 and IL4. The cDNA of equine IL2 or IL4 was cloned in a mammalian expression vector, containing c-terminal myc- and six histidines His(6)-epitopes for recognition and purification of equine cytokines. The vector constructs were used for transfection of chinese hamster ovary (CHO) cells. Purified equine cytokines were characterised by western blotting. Equine IL2 was secreted with a molecular weight of approximately 17.1kDa, whereas IL4 was expressed in three different sizes of 17.1, 19.6 and 22.1kDa, probably due to different glycosylation modifications. The biological activities of both cytokines were tested by proliferation assays using leukoagglutinin (LAG) prestimulated equine PBMC. Both, equine IL2 and IL4 induced dose-dependent lymphocyte proliferation. In contrast to IL4, IL2 supported the proliferation of B cells.

Modulation of lympho-proliferative responses of ovine peripheral blood mononuclear cells by Mycoplasma mycoides ssp. mycoides (LC type)

The present study was carried out to investigate the immunomodulating potential of M. mycoides ssp. mycoides (Mmm) (LC): a standard strain (Y-Goat, YG) and a local strain (M30) isolated from the pneumonic lung of a lamb during an outbreak of respiratory disease. The study was conducted in two parts to determine in vitro and in vivo aspects of the Mmm-induced modulation of cellular immune responses. In vitro experiments, using peripheral blood mononuclear cells (PBMC) of naive lambs, showed that live (Lv) or inactivated (Ina) antigens of Mmm (strains YG and M30) were not mitogenic for PBMC. Live antigens of both the strains, however, induced significant suppression of the PHA-driven lympho-proliferative (LP) responses. Suppression of LP responses by infectious Mmm (both strains) was restored in the presence of exogenous recombinant human interleukin-2 (rhIL-2). Following experimental inoculation of lambs with Mmm (YG), a significant reduction in non-specific LP responses was observed on days 6, 10 and 14 post inoculation (p.i.). There was a slow but significant rise in memory LP responses to Mmm strains (YG and M30). Specific subset depletion studies, using immunomagnetic cell separation (IMCS) technique, carried out on days 10 and 14 p.i., revealed that the OvCD4+ cell population was the main proliferating lymphocyte subset following an infection with Mmm (LC type).

Porcine cytokines

Cytokines play a central role in modulation of immunological and physiological processes in animals under both homeostatic and abnormal conditions. Currently available information from a variety of species indicates that interleukins, interferons and tumor necrosis factor mobilize immune responses, activate inflammatory reactions and communicate with organ systems; colony stimulating factors regulate hematopoiesis and hematopoietic cell function; transforming growth factor beta affects wound healing, bone remodeling and cellular differentiation. Our understanding of cytokine biology in pigs is selective and based largely on effects of human proteins in porcine models of human diseases. However, knowledge of the nature and role of cytokines in swine immunology and physiology is increasing rapidly due to the application of molecular cloning techniques to porcine cytokines. This review summarizes the current state of knowledge of porcine cytokines and focuses on biological processes in which the porcine proteins have been investigated in swine.

Cloning and expression of bovine and porcine interleukin-2 in baculovirus and analysis of species cross-reactivity

The cDNAs encoding bovine and porcine interleukin-2 (IL-2) have been expressed using the baculovirus Autographa californica nuclear polyhedrosis virus as a vector in insect cells. Insect cells infected with recombinant viruses secreted bovine and porcine IL-2 into the culture medium, with biological activities for maintaining the proliferation of homologous cells. When the activities of these two IL-2 proteins and commercially available human IL-2 were tested on heterologous cells differences were found. Recombinant bovine (rb)IL-2 only supported the growth of bovine lymphocytes and was not active on human, mouse or porcine lymphocytes. Recombinant porcine (rp)IL-2 and recombinant human (rh)IL-2 supported the proliferation of human, bovine, porcine and murine cells. However, the proliferative response of human lymphocytes to rpIL-2 was only 50% of that seen with rhIL-2. Sequence differences at the predicted p55 and p75 contact binding sites may explain this.

Molecular cloning and expression of equine interleukin 2

We have cloned equine IL-2 cDNA in vitro using the polymerase chain reaction (PCR) and primers based on the human IL-2 sequence. The cloned product appears to contain the entire coding region for equine IL-2 based on homology with other known sequences. When expressed in COS cells, the recombinant product augmented the proliferative response of equine peripheral blood mononuclear cells to concanavalin A, however, it failed to support the continued proliferation of murine CTLL-2 cells. Specific substitutions in those regions associated with p55 and p75 binding appear to account for this species-specifity.

Recombinant human interleukin 2 induces proliferation and immunoglobulin secretion by bovine B-cells: tissue differences and preferential enhancement of immunoglobulin A

Recombinant human interleukin 2 (rhIL2) was found to have activity on bovine B-cells in vitro, inducing both their proliferation and differentiation into immunoglobulin secreting cells. Only low and medium density (activated) B-cells were responsive; high density (resting) B-cells did not respond to rhIL2. Proliferative responses by unfractionated and purified B-cell populations were similar for all tissues tested. In contrast, immunoglobulin secretion was stimulated to a greater degree in prescapular lymph node (PSLN) and bronchial lymph node (BLN) cells than in mesenteric lymph node (MLN) cells and splenic lymphocytes on culture with IL2. All isotypes were stimulated equally in the case of PSLN, BLN, and splenic lymphocytes. However, culture of unfractionated MLN lymphocytes with IL2 resulted in enhanced secretion of IgA relative to the other isotypes. Removal of T-cells and accessory cells from the MLN lymphocyte preparation resulted in this effect being lost.

A monoclonal antibody recognising an epitope associated with pig interleukin-2 receptors

A monoclonal antibody is described which recognises an epitope associated with a receptor for interleukin-2 (IL-2) on pig lymphocytes. The monoclonal antibody inhibits high affinity binding of radiolabelled recombinant human IL-2 (rhIL-2) by pig lymphoblasts and also non-competitively inhibits both pig-TCGF and rhIL-2 maintained proliferation. By flow cytometry the antigen is apparently not present on freshly isolated blood lymphocytes but is detectable on small cells between 6 and 12 h after activation and on large cells by 24-h. These findings are comparable with those obtained using monoclonal antibodies recognising the 55 kDa alpha chain of the human and mouse IL-2 receptor (p55, TAC) expressed on activated cells in vivo and in vitro. However, the molecular weight of the porcine antigen is between 65 and 70 kDa.

Proliferative response of mammary gland mononuclear cells to recombinant bovine interleukin-2

Methods of augmenting bovine mononuclear cell responsiveness during physiological transitions of the udder may enhance resistance of the mammary gland to intramammary infections. Interleukin-2 is required for proliferation of T-lymphocytes and may contribute to B-lymphocyte proliferation. Recombinant bovine interleukin-2 (rBoIL-2) was evaluated as a potential immunoenhancer of bovine mammary gland mononuclear cells. Bovine mononuclear cells were isolated from five primiparous Holstein cows at 14-18 and 28-32 days of involution and at 7-13 days prior to parturition. Bovine blood and mammary gland mononuclear cells were highly responsive to rBoIL-2. Response of mammary gland mononuclear cells to rBoIL-2 was comparable with response of blood mononuclear cells. These data suggest that rBoIL-2 may be an effective immunoenhancer of bovine mononuclear cells during the non-lactating and prepartum periods.

Cervine T-lymphocyte growth factors and their measurement in tuberculosis

Research into the composition and function of the immune response in domesticated ruminants has tended to focus on the ovine and bovine systems. With the recent domestication of deer, health problems have developed which require a fundamental knowledge of the immune function in exotic ruminants. In this report it is shown that although recombinant human and mouse interleukin-2 (IL-2) were capable of stimulating cervine T-cell proliferation, optimal proliferation was only achieved using recombinant bovine IL-2. While some phylogenetic restriction of IL-2 cross-reactivity was found, in some cases this could be overcome by using high concentrations of recombinant IL-2. Using cervine T-cell blasts it was possible to assay in vitro T-cell growth factor (TCGF) production by lymphocytes isolated from deer naturally exposed to tuberculosis Mycobacterium bovis). Differences were found in the amount of TCGF present in the supernatants of antigen-activated cells isolated from severely diseased animals, those with limited disease and non-diseased animals.

In vitro mitogen responses and lymphocyte subpopulations in cheetahs

Lack of genetic variability and apparent susceptibility of cheetahs (Acinonyx jubatus jubatus) to coronavirus infection has lead to speculation that this species may have immune system deficits. To establish a foundation for evaluation of the immune function, cheetah peripheral blood mononuclear cells (PBM) were stimulated by a panel of six mitogens, and responses compared with those of domestic cat PBM. Individual responses in both species were variable, but evenly distributed throughout the range of stimulation for each mitogen. Proliferation by PBM from domestic cats occurred within the same range as that of the cheetahs. However, a significantly lower response to peanut agglutinin (PNA) was observed with domestic cat PBM. Although responses varied between animals, certain individual cheetahs were consistent low responders. The decreased values could not be explained by lack of IL-2 responsiveness since exogenous IL-2 significantly enhanced mitogen-stimulated proliferation in 11 of 12 cheetahs tested. The phenotypic distribution of domestic cat and cheetah lymphocyte subpopulations was similar as assessed by immunofluorescence staining for surface immunoglobulin (sIg) and cytotoxic T (Tc) cells (using a specific monoclonal antibody, FT2). Values for B cells (31.2% sIg+) and Tc (28.7% FT2+) were slightly higher in domestic cats as compared with cheetah PBM (13.3% sIg+; 19.0% FT2+). Even though no species-specific deficits were detected, a significant negative correlation between PHA-stimulated proliferation and percent FT2+ (Tc) cheetah cells was observed. This indicates that proliferation can be used indirectly to assess relative numbers of functional T helper cells in cheetahs. Our studies suggest that these aspects of the cheetah's immune system are comparable with the domestic cat, and establish a basis for in vitro assays evaluating antigen-specific responses.

Cytokines: applications in domestic food animals

Cytokines such as human, bovine, and porcine interferons and human and bovine interleukin-1 and interleukin-2 have been used in vivo in cattle and pigs. Colony-stimulating factors and tumor necrosis factor alpha have been evaluated in vitro in food animals. Studies to evaluate cytokines in domestic food animals have shown that specific and nonspecific immunomodulation is possible in immunosuppressed or pathogen-exposed animals. Cytokine prophylaxis or therapy in food animals may have the greatest potential for control of respiratory disease and mastitis.

Bovine recombinant interleukin-2 augments immunity and resistance to bovine herpesvirus infection

The in vivo administration of bovine recombinant interleukin-2 (rIL-2) was evaluated in calves vaccinated and then challenged with bovine herpesvirus-1 (BHV-1). In Experiment 1, 24 calves were allotted to four groups: control; bovine rIL-2; BHV-1 vaccine (modified-live); and bovine rIL-2 + BHV-1 vaccine. Serum neutralizing antibody titers to BHV-1 were increased sixfold, and virus shedding was fourfold less in calves vaccinated and treated with rIL-2 (25 micrograms/kg, intramuscularly) when compared to calves that received vaccine only. Treatment with rIL-2 induced lymphokine-activated killer activity that was eliminated by pretreating effector cells with complement and a monoclonal antibody (B26A) specific for the sheep red blood cell receptor. The rIL-2 treatment in BHV-1-vaccinated calves increased the calves' ability to withstand a BHV-1 challenge. However, during treatment with rIL-2, calves developed diarrhea and mild fever that abated after IL-2 treatment was stopped. A second experiment was then conducted to determine a dose of rIL-2 that would enhance immunity to BHV-1 without causing adverse side effects. Twenty-five calves were allotted to five groups that received injections of rIL-2 at 0.0, 25.0, 2.5, 0.25, or 0.025 micrograms kg-1 day-1 for 5 days. All calves received a modified-live BHV-1 vaccine. Calves treated with 25.0 micrograms kg-1 day-1 showed similar adverse side effects as in the first experiment but all other calves were normal. Compared to control calves, those treated with 25.0, 2.5, and 0.25 micrograms kg-1 day-1 of rIL-2 had higher (P less than 0.05) serum antibody titers to BHV-1 and following challenge lower (P less than 0.05) BHV-1 titers in nasal secretions; additionally, clinical disease as evidenced by nasal and ocular discharge was less severe (P less than 0.05). In vitro cytotoxic responses against BHV-1-infected bovine kidney cells were increased (P less than 0.05) in calves treated with rIL-2 in a dose dependent manner. These data suggest that bovine rIL-2 at 2.5 to 0.25 micrograms/kg may be an effective adjuvant to immunization.

The effect of human recombinant interleukin-2 on the porcine immune response to a pseudorabies virus subunit vaccine

The effect of human recombinant interleukin-2 (rIL-2) as an immune enhancing agent was evaluated in pigs vaccinated with a pseudorabies virus subunit vaccine (SV). Two groups of three pigs received two 25 micrograms doses of SV given 3 weeks apart. One group received 10(5) kg-1 day-1 of rIL-2 subcutaneously over two 5-day periods beginning on the day of the first and second vaccine inoculation. Six other pigs were immunized with two 5 micrograms doses of SV. Three of these pigs were treated as above with rIL-2. The effect of treatment was evaluated by comparing: the humoral response; the cell-mediated immune (CMI) response as measured by lymphocyte blastogenesis before and after virus challenge; and the weight response and virus excretion pattern after challenge with virulent pseudorabies virus (PRV). The humoral antibody response as detected by the serum virus neutralization (SN) assay and the enzyme linked immunosorbent assay (ELISA) was consistently higher in rIL-2 treated pigs than in non-treated pigs. These differences were significant (P less than 0.05) among high vaccine dose pigs prior to virus challenge when measured by the SN assay and during the anamnestic response period between days 3 and 10 after challenge when measured by both the SN assay and the ELISA. No differences were detected between treatment groups in the weight response, virus excretion pattern or the CMI response. These results suggest that human rIL-2 may have enhanced the immune response of pigs to the subunit vaccine.

Local interleukin-2 therapy in bovine ocular squamous cell carcinoma. A pilot study

Five cows bearing bovine ocular squamous cell carcinoma (BOSCC) were treated with low doses of recombinant human interleukin-2 (rhIL-2). A dose of 2500 U rhIL-2 was injected intralesionally and another 2500 U were injected into the subparotid regional lymph node once a day during a period of 5 consecutive days. This cycle of 5 days was repeated after an interval of 2 days. Total regression of the tumor was observed in three out of five animals. One cow showed tumor regression (greater than 80%) accompanied by metastases to the regional lymph node that were observed from the fifth week after the beginning of the treatment. Growth of the tumor of the fifth animal was retarded after treatment. In vitro proliferation of peripheral blood lymphocytes was investigated in two animals and tumor-infiltrating lymphocytes in one animal during incubation in various rhIL-2 concentrations. Cytotoxic activity of both cell populations against P815, Yac-1 and BOSCC-derived cell lines increased during incubation with rhIL-2. Cultured BOSCC-infiltrating lymphocytes showed predominant killing of the BOSCC-derived autologous cell line after 4 weeks of culture. Preliminary phenotype analysis did not give conclusive results with respect to the types of cells responsible for killing.

Human recombinant interleukin-2(125) induced in vitro proliferation of equine, caprine, ovine, canine and feline peripheral blood lymphocytes

Equine, caprine, ovine, canine and feline peripheral blood lymphocytes were evaluated in a short term dose-response study for their in vitro blastogenic responsiveness to human recombinant interleukin-2(125) (HrIL-2(125] alone or in combination with phytohemagglutinin-P, concanavalin-A, and pokeweed mitogen. HrIL-2(125) induced lymphocyte proliferation in all of the animals tested. The magnitude of the proliferative response varied among the species of animal tested. In all cases the proliferative response was dependent on the concentration of HrIL-2(125). HrIL-2(125) at a minimum concentration of 10(2) Cetus Units (CU)/ml produced a significant proliferative response in isolated horse, goat and sheep lymphocytes. In cat and dog lymphocytes, a concentration of 10(3) CU/ml was necessary to induce a significant proliferative response. Maximal lymphocyte proliferation was reached in horses and sheep at a concentration of 10(4) CU/ml of HrIL-2(125). In goats, cats, and dogs a maximum proliferative response was found to be at a concentration equal to or greater than 10(4) CU/ml of HrIL-2. Co-stimulation of lymphocytes with mitogens and submaximal concentrations of HrIL-2(125) (10 CU/ml) induced a synergistic proliferative response which in nearly all cases was significantly greater (P less than 0.05) than the arithmetic sum of the responses induced by the same concentration of the mitogens and HrIL-2(125) alone. The two exceptions were co-stimulation of feline lymphocytes with concanavalin-A and co-stimulation of canine lymphocytes with pokeweed mitogen.

Establishment and initial characterization of continuous in vitro cultures of bovine T lymphocytes

Utilizing human recombinant interleukin 2 (HrIL-2) in combination with several mitogens, continuously growing cultures of bovine lymphocytes have been established. Continuous presence of HrIL-2 is required to maintain the growth of these cultures but a requirement for continued presence of mitogen seems variable. Cloned lines have been derived from these cultures by limiting dilution and outgrowth in the presence of mitomycin C treated bulk cells. Cell surface phenotype analysis indicates that all of these cultures and cloned lines are of the T cell lineage. Functional analysis indicated that some of these cultured cells are cytolytically active in lectin mediated assays whereas others are not. Utilization of this technology for the growth and characterization of bovine T cells will undoubtedly contribute to an enhanced understanding of the bovine immune response mechanisms.