Reconstitution of antibody-dependent phagocytosis in fibroblasts expressing Fc gamma receptor IIIB and the complement receptor type 3

In this study, we test the hypothesis that co-expression of both the complement receptor type 3 (CR3; CD11b/CD18) and Fc gamma receptor type IIIB (Fc gamma RIIIB) (CD16) are sufficient to mediate Ab-dependent phagocytosis. To explore the roles of these receptors in a simple and well-defined in vitro system, stable transfectants of fibroblasts expressing either CR3, Fc gamma RIIIB, or the combination of CR3 and Fc gamma RIIIB were generated. Cells not expressing either receptor, but exposed to the transfection protocol, were used as controls. Cell surface expression of CR3 and/or Fc gamma RIIIB were confirmed by using both flow cytometry and epifluorescence microscopy. The cell lines were analyzed for their ability to bind and internalize opsonized erythrocytes. Cells expressing both CR3 and Fc gamma RIIIB were able to both bind and phagocytose IgG-coated erythrocytes. In contrast, cells expressing CR3 only were able to phagocytose yeast, but not to bind nor phagocytose IgG-coated erythrocytes. Similarly, cells expressing Fc gamma RIIIB only were able to bind IgG-coated erythrocytes, but not to phagocytose either the erythrocytes or yeast. These studies demonstrate that, although CR3 does not participate in Ab-dependent recognition, it can complement the function of Fc gamma RIIIB to effect Ab-dependent phagocytosis. These studies also suggest that one mechanism for glycosylphosphatidylinositol-linked proteins to mediate intracellular functions is through interactions with transmembrane proteins.

Liquid-crystal light valves as thresholding elements in neural networks: basic device requirements

An important device for optoelectronic neural networks is a two-dimensional nonlinear thresholding element that is optically written and optically read. The liquid-crystal light valve is the only commercially available device that is suitable for this application. Three different types of valve are analyzed with respect to their suitability for two different types of neural network.

Physical association of complement receptor type 3 and urokinase-type plasminogen activator receptor in neutrophil membranes

A previous study has shown that Fc gamma RIIIB (CD16), an extensively glycosylated glycosyl-phosphatidylinositol-linked neutrophil membrane protein, specifically co-caps with the iC3b R (CR3; CD11b/CD18). This study tests the possible physical interactions of another extensively glycosylated glycosyl-phosphatidylinositol-linked protein, the urokinase-type plasminogen activator receptor (uPAR), with CR3. Receptors were labeled using fluorochrome-conjugated F(ab')2 fragments of an anti-CR3 mAb. In some cases cells were capped using second step F(ab')2 fragments of an anti-mouse F(ab')2 antiserum. After 30 min at 37 degrees C, 65 +/- 4% of the cells exhibited CR3 caps whereas 61 +/- 2% demonstrated uPAR caps. When CR3-capped cells were probed with F(ab')2 fragments of anti-uPAR conjugated to a distinct fluorochrome, 45 +/- 3% of the cells co-capped uPAR. When uPAR was capped, 48 +/- 2% of the cells co-capped CR3. Similar levels of co-capping were observed using a DNP-conjugated anti-CR3 F(ab')2 and an anti-DNP second step F(ab')2 reagent for capping or using FITC-uPA as a probing reagent. Furthermore, CR3-uPAR co-capping and/or co-clustering was also observed using anti-CR3 IgM and Mn2+ as integrin aggregation stimuli. Significant co-capping of anti-CD14, anti-CD59, anti-Mo5, anti-HLA, or NBD-PE (a lipid probe) was not observed. Moreover, CR3 and uPAR co-capping was blocked by N-acetyl-D-glucosamine, but not by six other saccharides, suggesting that a lectin-like site may participate in co-capping. This suggests that CR3 may regulate adhesive events by several mechanisms, including the regulation of the spatial distribution of uPAR.

Tissue distribution of DNA adducts of 7H-dibenzo[c,g]carbazole and its derivatives in mice following topical application

7H-Dibenzo[c,g]carbazole (DBC) is a potent liver and skin carcinogen following topical administration. The objective was to determine the pattern of DBC-DNA adducts produced in both target and nontarget tissues when DBC and its metabolites were applied topically at carcinogenic doses. DBC phenolic derivatives 1-hydroxy-DBC, 2-hydroxy-DBC, 3-hydroxy-DBC, 4-hydroxy-DBC, 5-hydroxy-DBC, 6-hydroxy-DBC, 13-c-hydroxy-DBC, and N-methyl-DBC were applied dermally to Hsd:ICR (Br) mice. Tissues were harvested 24 h later, and DBC-DNA adduct levels were determined by 32P-postlabeling. The levels of DBC-DNA adducts were about 25 times greater in liver than in any other tissue. Total DBC-DNA adducts were seen in skin and lung at about equal levels, while adduct levels in kidney and other tissues were no more than one fourth that of lung and skin. Adduct 6 was the predominant adduct in liver, adducts 2 and 3 were formed preferentially in skin, and adduct 3 was formed preferentially in lung. 3-Hydroxy-DBC and 4-hydroxy-DBC produced higher levels of DNA adducts in skin, lung, and liver than did the parent compound or 2-hydroxy-DBC. DNA adducts were not seen in any tissue for the 1-, 5-, 6-, or 13-c-hydroxy compounds. In addition, hepatic DNA adducts were not seen when the nitrogen of DBC was methylated. In lung and skin, N-methyl-DBC induced DNA adducts at levels comparable to DBC, although the adduct profile in these tissues was different from that of DBC itself.(ABSTRACT TRUNCATED AT 250 WORDS)

Physical association of complement receptor type 3 and urokinase-type plasminogen activator receptor in neutrophil membranes

A previous study has shown that Fc gamma RIIIB (CD16), an extensively glycosylated glycosyl-phosphatidylinositol-linked neutrophil membrane protein, specifically co-caps with the iC3b R (CR3; CD11b/CD18). This study tests the possible physical interactions of another extensively glycosylated glycosyl-phosphatidylinositol-linked protein, the urokinase-type plasminogen activator receptor (uPAR), with CR3. Receptors were labeled using fluorochrome-conjugated F(ab')2 fragments of an anti-CR3 mAb. In some cases cells were capped using second step F(ab')2 fragments of an anti-mouse F(ab')2 antiserum. After 30 min at 37 degrees C, 65 +/- 4% of the cells exhibited CR3 caps whereas 61 +/- 2% demonstrated uPAR caps. When CR3-capped cells were probed with F(ab')2 fragments of anti-uPAR conjugated to a distinct fluorochrome, 45 +/- 3% of the cells co-capped uPAR. When uPAR was capped, 48 +/- 2% of the cells co-capped CR3. Similar levels of co-capping were observed using a DNP-conjugated anti-CR3 F(ab')2 and an anti-DNP second step F(ab')2 reagent for capping or using FITC-uPA as a probing reagent. Furthermore, CR3-uPAR co-capping and/or co-clustering was also observed using anti-CR3 IgM and Mn2+ as integrin aggregation stimuli. Significant co-capping of anti-CD14, anti-CD59, anti-Mo5, anti-HLA, or NBD-PE (a lipid probe) was not observed. Moreover, CR3 and uPAR co-capping was blocked by N-acetyl-D-glucosamine, but not by six other saccharides, suggesting that a lectin-like site may participate in co-capping. This suggests that CR3 may regulate adhesive events by several mechanisms, including the regulation of the spatial distribution of uPAR.

Aberrant capping of membrane proteins on neutrophils from patients with leukocyte adhesion deficiency

Several functional defects have been found in neutrophils from leukocyte adhesion deficiency (LAD) patients who fail to express the CD11/CD18 leukoadhesins: Mo1, LFA-1, and p150,95. To better understand the functional defects of LAD neutrophils, we have performed capping experiments. Purified normal or LAD neutrophils were labeled with fluorochrome-conjugated concanavalin A (Con A) or F(ab')2 fragments of antiurokinase-type plasminogen activator receptor (uPAR), anti-Fc gamma RIII (CD16), anti-Mo5, and anti-CD14 antibodies. F(ab')2-labeled cells were capped using a second-step F(ab')2 fragment of an antimurine Fab antiserum. Cells were capped for 30 minutes at 37 degrees C, then observed by fluorescence microscopy. LAD neutrophils were found to be deficient in capping, but not clustering of all of the reagents tested to date. The percent of cells exhibiting capping of Con A, Fc gamma RIII, urokinase receptor, CD14, and Mo5 were 52%, 67%, 70%, 25%, and 64% for normal neutrophils but were only 10%, 5%, 2%, 3%, and 1%, respectively, for LAD neutrophils. Capping of this panel of membrane components in LAD or normal neutrophils was not augmented by the addition of either 10(-5) mol/L colchicine or 10(-7) mol/L FMLP. Because capping requires membrane-to-cytosol communication and an intact microfilament linkage, we suggest that leukoadhesins may play a broad role in promoting the redistribution of membrane components including adherence-related receptors such as Fc gamma RIII and the urokinase receptor.

Immune response to bovine viral diarrhea virus induced by anti-idiotypic antibodies

We have previously prepared rabbit anti-idiotypic antibodies (anti-Ids) against the neutralizing monoclonal antibodies (MAbs) specific for the gp53 of bovine viral diarrhea virus (BVDV). The anti-Ids, purified by sequential immunoaffinity chromatography, inhibited the immunizing MAb from binding to the original antigens and blocked BVDV infection of cell cultures. This study evaluated immune responses in mice to the purified anti-Id reagents. BVDV-specific neutralizing antibodies were induced by the anti-Ids. The antisera (Ab3) induced by the anti-Ids immunoprecipitated gp53 from BVDV-infected Madin-Darby bovine kidney (MDBK) cell lysates. However, lymphocyte-proliferative responses were specific only for the respective immunizing antigens. These results suggest that the anti-Ids may bear an internal image of the gp53 to stimulate production of antibody but not to stimulate a virus-specific cellular immune response in mice.

Immunopotentiation of bovine respiratory disease virus vaccines by interleukin-1 beta and interleukin-2

Three experiments, using 85 crossbred beef calves, were conducted to evaluate the adjuvanticity of single, multiple, and combined doses of recombinant bovine IL-1 beta (rBoIL-1 beta) and recombinant bovine IL-2 (rBoIL-2), with a modified-live bovine herpesvirus-1/parainfluenza-3 (BHV-1/PI-3) virus vaccine and a killed bovine viral diarrhea (BVD) virus vaccine. Cytokines were administered intramuscularly at vaccination but at different injection sites. All cytokine treatments increased non-major histocompatibility complex (MHC)-restricted cytolytic capability of peripheral blood mononuclear cells (PBMC) against virus-infected target cells and serum neutralizing (SN) antibody titers to BHV-1 and BVD virus. Multiple, consecutive injections of rBoIL-2 generally showed the greatest adjuvant effect, and no additive effect was observed when rBoIL-1 beta and rBoIL-2 were administered together. In a challenge experiment, calves were vaccinated with a modified-live BHV-1/PI-3 vaccine and infected with BHV-1 on Day 21. Cytokine-treated calves had higher SN antibody titers to BHV-1 than did the control calves at the time of challenge. Calves that were administered rBoIL-2 on 5 consecutive days shed less BHV-1 and had the highest SN antibody titer to BHV-1 (Day 28). These data suggest that rBoIL-1 beta and rBoIL-2 may be useful immunoadjuvants for bovine respiratory disease virus vaccines.

Acetylation of phenolic derivatives of 7H-dibenzo[c,g]carbazole: identification and quantitation of major metabolites by rat liver microsomes

Acetylation stabilized the phenolic metabolites of 7H-dibenzo[c,g]carbazole (DBC) and made it possible to accumulate greater amounts of metabolites for comprehensive chemical structural elucidation and quantification without the use of radiolabeled DBC. High-resolution mass spectral data and 1H NMR and fluorescence spectra were used to confirm the existence of 5-OH-DBC, 3-OH-DBC, 1-OH-DBC, and the oxidative dimer, 6,6'-bis-(5-OH-DBC), in the acetylated metabolite mixture formed in vitro by 3-methylcholanthrene-induced rat liver microsomes. Using the synthesized acetoxy-DBC derivatives as standards, the HPLC external standard method was employed for quantitation of the major DBC metabolites after acetylation. The quantities of 5-OH-DBC, 3-OH-DBC, 1-OH-DBC, and DBC in the metabolite mixture determined using the external standard method were found to agree with those calculated using the radiometric method. Acetylation is a promising nonradiometric qualitative and quantitative technique for further metabolism studies of DBC and analogues which produce unstable monohydroxylated metabolites.

Characterization of secretin release in secretin cell-enriched preparation isolated from canine duodenal mucosa

The release of secretin was studied in secretin cell-enriched preparations isolated from canine duodenal mucosa. The crude enterocytes were isolated by treating the duodenal mucosa sequentially with collagenase and ethylenediaminetetraacetic acid. Secretin cell-enriched fraction was prepared by centrifugation of the crude enterocytes in a counterflow elutriation rotor to obtain a final preparation containing 3.2 +/- 0.3 pmol/10(6) cell of immunoreactive secretin, which was 13-fold greater than the crude cell preparation (N = 5). The cells were incubated in Hanks' balanced salt solution for 20 min at 37 degrees C under 95% O2/5% CO2 before adding various agents and further incubated for various periods of time. The amounts of secretin released into the medium and retained by the cells were then determined by a specific radioimmunoassay. The release of immunoreactive secretin was increased dose-dependently over the control by dibutyryl cyclic-3',5'-adenosine monophosphate, forskolin, 4 beta-12-O-tetradecanoylphorbol-13-acetate, the synthetic serine protease inhibitor, camostat, and the calcium ionophore, A23187. The effects of forskolin, the phorbol ester, and A23187 were time-dependent and not observed at 4 degrees C. The release of immunoreactive secretin was also stimulated by KCl in high concentration and by sodium oleate. The effect of A23187 was abolished in a Ca(2+)-free medium, while those of dibutyryl cyclic-3',5'-adenosine monophosphate and forskolin were potentiated by 3-isobutyl-1-methylxanthine, which did not have a significant effect when added alone. These results indicate that the release of secretin is regulated by both Ca(2+)- and cyclic-3',5'-adenosine monophosphate-dependent mechanisms.2+ release.

Identification of the cell surface receptor for bovine viral diarrhoea virus by using anti-idiotypic antibodies

We have produced and characterized polyclonal anti-idiotypic antibodies (anti-ids) that mimic the antigenic structures of gp53 from bovine viral diarrhoea virus (BVDV). In this study, the anti-ids were used to identify cell receptors for BVDV. The anti-ids bound specifically to bovine cells, as determined by flow cytometric analysis, and inhibitory binding assays showed that they bound to the cell surface receptors for BVDV. A cell surface protein with an M(r) of approximately 50K was immunoprecipitated by the anti-ids from MDBK cells; this was blocked by preincubation of cell lysate with BVDV. This indicates that the 50K protein might be a specific receptor for BVDV gp53. Thirteen BVDV strains were used to evaluate inhibition of anti-id binding to MDBK cells and inhibition of BVDV infection of anti-id-treated MDBK cell monolayers. Results demonstrated that both processes were inhibited to varying degrees depending on virus strain. The results suggested that multiple receptors for BVDV attachment may exist on MDBK cells, and that different virus strains do not have the same receptor.

Comparison of bovine immune responses to affinity-purified bovine herpesvirus-1 antiidiotypes and glycoproteins

Bovine immune responses to rabbit antiidiotypic antibodies (anti-Id) against neutralizing monoclonal antibodies to bovine herpesvirus-1 (BHV-1) envelope glycoproteins and to BHV-1 glycoproteins were compared. Glycoprotein-immunized animals produced high titers of anti-BHV-1 antibodies and were protected against BHV-1 challenge. Recombinant bovine interleukin-2 (rIL-2)-treated, anti-Id-immunized animals showed a slight reduction in clinical disease, and one calf produced BHV-1-neutralizing antibodies. Treatment with rIL-2 augmented non-BHV-1-specific immune responses. However, even with rIL-2 as an adjuvant, the mixture of polyclonal anti-Id did not elicit a consistent, protective BHV-1-specific immune response in calves.

32P-postlabeling analysis of dibenz[a,j]acridine DNA adducts in mice: preliminary determination of initial genotoxic metabolites and their effect on biomarker levels

N-Heterocyclic aromatics (NHA) are widely occurring environmental pollutants formed during the pyrolysis of nitrogen-containing organic chemicals. NHA are found in significant amounts in tobacco condensates, synthetic fuels, gasoline engine exhaust, and effluents from the heating of coal. Dibenz[a,j]acridine (DBA) is an example of NHA. The potency of many carcinogenic compounds is related, at least in part, to the efficiency of their biological activation. We undertook studies to determine which initial metabolites of DBA lead to the formation of high levels of carcinogen-DNA adducts in vivo. DBA and its metabolites, trans-DBA-1,2-dihydrodiol (DBA-1,2-DHD), trans-DBA-3,4-dihydrodiol (DBA-3,4-DHD), and trans-DBA-5,6-dihydrodiol (DBA-5,6-DHD), were applied to the skin of mice. DNA was isolated using enzyme-solvent extraction method. DNA was 32P-postlabeled under conditions of limiting [32P]ATP. In skin, DBA produced two distinct adducts. The same two adducts were seen when DBA-3,4-DHD was applied. In addition the total adduct level elicited by DBA-3,4-DHD was higher than that of parent compound. Two adducts were seen when DBA-5,6DHD was applied, but these were very different from adducts seen with DBA. These results suggested that activation of DBA to DNA-binding compounds in skin includes initial formation of DBA-3,4-DHD. The data support development of biomarkers for the exposure and effect of this compound, and also suggest that specific metabolic susceptibility markers might be able to predict populations at increased risk.

Anti-idiotypic antibodies to bovine herpesvirus-1 inhibit virus infection in cell cultures

A panel of murine monoclonal antibodies (MAbs) to bovine herpesvirus-1 (BHV-1) was prepared. Three of them were neutralizing MAbs and reacted against 130/75/50 kDa, 77 kDa, or 97 kDa glycoproteins (gp). A fourth non-neutralizing MAb recognized the 97 kDa gp. Competition radioimmunoassay demonstrated that each of the four MAbs reacted against a different virus epitope. Anti-idiotypic antibodies (anti-id) to the four MAbs were produced in rabbits and purified by sequential immunoaffinity chromatography. Each anti-id inhibited the binding of its respective MAb to BHV-1 in competitive ELISA and blocked BHV-1 neutralizing activity of the MAb. This inhibition suggested that the anti-ids were specific for the antigen binding site of the MAbs. Treatment of MDBK cells with anti-ids inhibited BHV-1 infection, which suggested that the anti-ids block a cellular component essential for virus infection. Absence of significant cross-reactivity among the anti-ids for heterologous MAbs indicated that they recognized unique determinants on the antigen binding site of the homologous MAb.

In vitro inhibition of 5-lipoxygenase metabolite, leukotriene B4, in bovine mononuclear cells by bovine viral diarrhea virus

Bovine viral diarrhea (BVD) virus inhibited phytohemagglutinin (PHA)-, PHA plus phorbol-12-myristate-13 acetate (PMA)- or PHA plus calcium ionophore (A23187)-stimulated bovine peripheral blood mononuclear cell (PBMC) proliferation. Further, BVD-virus inhibited A23187-stimulated leukotriene B4 (LTB4) synthesis into the culture supernatants. Presence of exogenous LTB4 failed to reverse the BVD virus-induced immunosuppression. Our results suggest that BVD virus-induced immunosuppression is due to a factor that may be necessary to induce LTB4 synthesis for normal mononuclear cell proliferation.

Anti-idiotypic antibodies mimic bovine viral diarrhea virus antigen

Polyclonal rabbit anti-idiotypic antibodies (anti-ids) against two neutralizing murine monoclonal antibodies (mAbs) specific to a bovine viral diarrhea virus (BVDV) glycoprotein, 53 kDa, were produced, purified, and characterized. Each anti-id inhibited the binding of its respective mAb to BVDV antigen in a competitive ELISA and blocked the immunoprecipitation of the 53 kDa protein by the mAb. The anti-ids also inhibited the virus-neutralizing activity of their homologous mAbs. These results suggest that the anti-ids bear an internal image of a BVDV antigen and mimic neutralizing epitopes on the 53 kDa protein. Treatment of MDBK cells with the anti-ids inhibited BVDV infection, indicating that they block a cellular component, such as a virus receptor, required for virus adsorption or entry. Inhibition of the homologous mAb and lack of inhibition of the heterologous mAb indicate that the anti-ids are specific for the unique antigen-binding sites on the mAbs.

[Detection and characterization of antigen component of circulating immune complex in sera from patients with lung cancer by monoclonal and polyclonal antibodies]

A total of 117 serum samples from 58 patients with lung cancer, 29 patients with nonmalignant thoracic diseases and 30 healthy donors were tested and analyzed for antigen component in CIC with 5 McAbs and PcAb by Sandwich-ELISA. The results indicated that McAbs were reactive with lung cancer associated CIC (positive rates ranging from 20-32%), while PcAbs were reactive with CIC both from lung cancer patients and from those with non-malignant thoracic diseases (positive rates 45.7% and 41.4% respectively). A combined set using a panel of McAbs to detect CIC will give a higher positive rate (49.2%) than using a single McAb. We anticipate that the McAb-ELISA established in this study to detect antigen-specific CIC will be helpful in the clinical diagnosis and prognosis of lung cancer.

[Using two monoclonal antibodies to detect lung carcinoma associated antigen in the sera of patients with lung cancer by BA-ELISA]

In this study two McAbs (LC86aE4 and LC86aC5) were chosen to detect circulating lung carcinoma associated antigen (LAA) in serum samples from 58 patients with lung cancer, 29 patients with nonmalignant thoracic diseases and 30 healthy donors by biotin-avidin (BA)-ELISA. Our data indicate that BA-ELISA was specific, sensitive, reproducible and simple. The rates of positive detection of LAAE4 or LAAC5 alone were found to be higher (44.8% and 48.3% respectively) in patients with lung cancer than in those with nonmalignant thoracic diseases (13.7%) and in normal donors (6.7%) (P less than 0.01). Furthermore, the combined detection of LAAE4 and LAAC5 resulted in a higher positive rate (62.3%) in lung cancer patients. The clinical application of these McAbs and the assay in the diagnosis of lung cancer is discussed.

Induction of immune response to bovine herpesvirus-1 with anti-idiotypic antibodies

Previously, we prepared rabbit anti-idiotypic (anti-Id) antibodies against murine monoclonal antibodies (MAbs) specific for the major bovine herpesvirus-1 (BHV-1) envelope glycoproteins. Glycoprotein III (gIII) contains neutralization epitopes and may be the virus attachment protein. Anti-Id antibodies to a neutralizing MAb that reacts with gIII were purified by sequential immunoaffinity chromatography. Immune responses to the purified anti-Id reagent and BHV-1 were compared in mice. Both groups of mice produced BHV-1-specific neutralizing antibodies. However, lymphocyte proliferative responses and interferon and interleukin-2 production were specific for the respective immunizing antigens. These results suggest that the anti-Id reagent may bear an internal image of a B-cell-stimulating epitope of glycoprotein gIII; however, this epitope does not stimulate a virus-specific cellular immune response in mice.

Antigenic variations in bovine viral diarrhea viruses detected by monoclonal antibodies

Five murine monoclonal antibodies (MAbs) against the NADL strain of bovine viral diarrhea (BVD) virus were developed, identified, and characterized. Four of the MAbs were directed against a 53-kilodalton (kDa) viral protein, and one was specific to a 47-kDa polypeptide. Competitive radioimmunoassay showed that two MAbs were specific to related epitopes of the 53-kDa protein, and the other three MAbs were each specific to a different epitope. The MAbs were used to study heterogeneity among BVD virus strains. Various degrees of reactivity of cytopathic and noncytopathic virus isolates were detected by virus neutralization and immunofluorescence assays. The virus isolates were divided into six groups based on the neutralization test. The results indicated that the 53-kDa glycoprotein of BVD virus is the major protein involved in virus neutralization and that only a few epitopes of the protein contribute to the neutralization. None of the MAbs neutralized all the BVD virus isolates tested in this study, suggesting antigenic variations among BVD virus isolates.

In vitro interactions of cytokines and bovine viral diarrhea virus in phytohemagglutinin-stimulated bovine mononuclear cells

Bovine viral diarrhea (BVD) virus inhibited phytohemagglutinin (PHA)-stimulated bovine peripheral blood mononuclear cell (PBMC) proliferation and bovine interleukin-2 (IL-2) production. In the controls, the heat-inactivated BVD virus was not capable of suppressing the PHA-stimulated PBMC proliferation. Presence of exogenous cytokines, such as purified human IL-2, recombinant bovine interleukin-1 (rbovIL-1), recombinant bovine IL-2, and recombinant human IL-6 failed to reverse the BVD virus-induced immunosuppression. Also, we found that the BVD virus inhibited PHA and IL-2 induced proliferation of bovine PBMC in the early and late stages of activation. In summary, our data suggest that BVD virus induced immunosuppression was not due to destruction of the PBMC but may be inhibiting one or more of the important intracellular enzymes that may regulate PBMC proliferation.