Comparison of recombinant Culicoides allergens produced in different expression systems for IgE serology of insect bite hypersensitivity in horses of different origins

Insect bite hypersensitivity (IBH) is an allergic dermatitis of horses, an IgE-mediated reaction to Culicoides midges. Causative Culicoides spp. are not indigenous in Iceland resulting in high prevalence of IBH in horses born in Iceland and exported as compared to Icelandic horses born in a Culicoides rich environment. The aims were (i) to compare IgE levels in sera of IBH-affected horses born in Iceland (n = 47) with horses of the Icelandic breed (n = 23) and of other breeds (n = 27) born in Culicoides infested area; (ii) to investigate if barley could be a useful production system of allergens for IBH immunoassays. IgE binding in sera was tested by ELISA on two recombinant Culicoides allergens, rCul n 3 and rCul n 4, each produced in E. coli, insect cells and barley. Significantly more IgE was detected against all allergens in sera from IBH-affected compared to healthy horses. Icelandic-born Icelandic horses stand out with higher IgE levels against the allergens and higher area under the curve (AUC) on rCul n 4 as compared to the European-born horses. The barley and E.coli produced allergens had very similar performance in distinguishing between IBH-affected and healthy horses.

New Strategies for Prevention and Treatment of Insect Bite Hypersensitivity in Horses

Purpose of Review

Treatment of equine insect bite hypersensitivity (IBH) needs to be improved. Allergen-specific immunotherapy (ASIT), the only curative treatment of allergy, currently has only a limited efficacy for treatment of IBH. This review highlights the latest findings in prophylactic and therapeutic strategies.

Recent Findings

Prophylactic vaccination against IBH using recombinant Culicoides allergen has been developed in unexposed Icelandic horses and is ready to be tested. Therapeutic virus-like particle (VLP)–based vaccines targeting equine interleukin- (IL-) 5 or IL-31 improved clinical signs of IBH by induction of anti-cytokine antibodies thus reducing eosinophil counts or allergic pruritus, respectively.

Summary

First studies for development of ASIT using pure r-Culicoides allergens have yielded promising results and need now to be tested in clinical studies for both prevention and treatment of IBH. Therapeutic vaccines inducing neutralizing antibodies against IL-5 or IL-31 will be valuable future treatments for reduction of clinical signs of IBH.

Barley produced Culicoides allergens are suitable for monitoring the immune response of horses immunized with E. coli expressed allergens

Insect bite hypersensitivity is an allergic dermatitis of horses caused by bites of Culicoides midges. Sufficient amount of pure, endotoxin-free allergens is a prerequisite for development and monitoring of preventive and therapeutic allergen immunotherapy. Aims of the study were to compare the Culicoides nubeculosus (Cul n) allergens Cul n 3 and Cul n 4, produced in transgenic barley grains with the corresponding E. coli or insect cells expressed proteins for measuring antibody and cytokine responses. Allergen-specific IgG responses were measured by ELISA in sera from twelve horses not exposed to Culicoides, before and after vaccination with E. coli-rCul n 3 and 4. Before vaccination no IgG binding to the barley and insect cell produced proteins was detected and a similar increase in specific IgG was observed after vaccination. While IgG levels to the E.coli expressed proteins were higher in the post-vaccination sera, some background binding was observed pre-vaccination. In vitro re-stimulation of PBMC was performed for measurements of cytokines. E. coli expressed proteins resulted in high background in PBMC from non-vaccinated controls. The barley and insect cell expressed proteins induced similar amount of IFN-γ and IL-4 in PBMC from vaccinated horses. Barley produced allergens are promising tools for use in immunoassays.

Longitudinal analysis of allergen-specific IgE and IgG subclasses as potential predictors of insect bite hypersensitivity following first exposure to Culicoides in Icelandic horses

BACKGROUND

Insect bite hypersensitivity (IBH) is an allergic dermatitis of horses caused by bites of Culicoides spp. IBH does not occur in Iceland because of the absence of Culicoides, but the prevalence is high in horses imported from Iceland to environments where Culicoides are present.

HYPOTHESIS/OBJECTIVE

Test, in a longitudinal study before and after Culicoides exposure, whether a primary sensitizing Culicoides allergen can be identified and if an increase of allergen-specific immunoglobulin (Ig)E or IgG subclasses precedes clinical signs of IBH.

ANIMALS

Thirty two horses imported from Iceland to Europe; 16 developed IBH and 16 remained healthy.

METHODS

Determination of IgE and IgG subclasses against recombinant (r)-Culicoides allergens and Culicoides extract in sera taken before first exposure to Culicoides and yearly over a period of 3-4 years.

RESULTS

Before Culicoides exposure, there were no significant differences in Culicoides-specific serum IgE levels between horse that developed IBH or remained healthy. Culicoides exposure induced an individual IgE response pattern (to a median of 4.5 r-allergens) in the IBH but not in the healthy end-point group. The increase in serum IgE levels to Culicoides r-allergens was concurrent with the initial onset of clinical signs of IBH. IBH-affected horses displayed significantly higher allergen-specific IgG1 and IgG5 levels than healthy controls. Recombinant Culicoides obsoletus 1 (Cul o1) and Cul o3-specific IgG5 was significantly higher in the IBH compared to the healthy end-point group, before clinical signs of IBH.

CONCLUSION/CLINICAL RELEVANCE

Allergen-specific serum IgE cannot be used as predictor for IBH, whereas allergen-specific IgG5 levels may have a predictive value.

A preventive immunization approach against insect bite hypersensitivity: Intralymphatic injection with recombinant allergens in Alum or Alum and monophosphoryl lipid A

Insect bite hypersensitivity (IBH) is an IgE-mediated dermatitis of horses caused by bites of Culicoides insects, not indigenous to Iceland. Horses born in Iceland and exported to Culicoides-rich areas are frequently affected with IBH. The aims of the study were to compare immunization with recombinant allergens using the adjuvant aluminum hydroxide (Alum) alone or combined with monophosphoryl lipid A (MPLA) for development of a preventive immunization against IBH. Twelve healthy Icelandic horses were vaccinated intralymphatically three times with 10 μg each of four recombinant Culicoides nubeculosus allergens in Alum or in Alum/MPLA. Injection with allergens in both Alum and Alum/MPLA resulted in significant increase in specific IgG subclasses and IgA against all r-allergens with no significant differences between the adjuvant groups. The induced antibodies from both groups could block binding of allergen specific IgE from IBH affected horses to a similar extent. No IgE-mediated reactions were induced. Allergen-stimulated PBMC from Alum/MPLA horses but not from Alum only horses produced significantly more IFNγ and IL-10 than PBMC from non-vaccinated control horses. In conclusion, intralymphatic administration of small amounts of pure allergens in Alum/MPLA induces high IgG antibody levels and Th1/Treg immune response and is a promising approach for immunoprophylaxis and immunotherapy against IBH.

Developing a preventive immunization approach against insect bite hypersensitivity using recombinant allergens: A pilot study

Insect bite hypersensitivity (IBH) is an allergic dermatitis of horses caused by bites of midges (Culicoides spp.). IgE-mediated reactions are often involved in the pathogenesis of this disease. IBH does not occur in Iceland due to the absence of Culicoides, but it occurs with a high frequency in Icelandic horses exported to mainland Europe, where Culicoides are present. We hypothesize that immunization with the Culicoides allergens before export could reduce the incidence of IBH in exported Icelandic horses. The aim of the present study was therefore to compare intradermal and intralymphatic vaccination using four purified recombinant allergens, in combination with a Th1 focusing adjuvant. Twelve horses were vaccinated three times with 10μg of each of the four recombinant Culicoides nubeculosus allergens. Six horses were injected intralymphatically, three with and three without IC31(®), and six were injected intradermally, in the presence or absence of IC31(®). Antibody responses were measured by immunoblots and ELISA, potential sensitization in a sulfidoleukotriene release test and an intradermal test, cytokine and FoxP3 expression with real time PCR following in vitro stimulation of PBMC. Immunization with the r-allergens induced a significant increase in levels of r-allergen-specific IgG1, IgG1/3, IgG4/7, IgG5 and IgG(T). Application of the r-allergens in IC31(®) adjuvant resulted in a significantly higher IgG1, IgG1/3, IgG4/7 allergen-specific response. Intralymphatic injection was slightly more efficient than intradermal injection, but the difference did not reach significance. Testing of the blocking activity of the sera from the horses immunized intralymphatically with IC31(®) showed that the generated IgG antibodies were able to partly block binding of serum IgE from an IBH-affected horse to these r-allergens. Furthermore, IgG antibodies bound to protein bands on blots of C. nubeculosus salivary gland extract. No allergen-specific IgE was induced and there was no indication of induction of IgE-mediated reactions, as horses neither responded to Culicoides extract stimulation in a sulfidoleukotriene release test, nor developed a relevant immediate hypersensitivity reaction to the recombinant allergens in skin test. IL-4 expression was significantly higher in horses vaccinated intralymphatically without IC31(®), as compared to horses intradermally vaccinated with IC31(®). Both routes gave higher IL-10 expression with IC31(®). Both intralymphatic and intradermal vaccination of horses with recombinant allergens in IC31(®) adjuvant induced an immune response without adverse effects and without IgE production. The horses were not sensitized and produced IgG that could inhibit allergen-specific IgE binding. We therefore conclude that both the injection routes and the IC31(®) adjuvant are strong candidates for further development of immunoprophylaxis and therapy in horses.

Evaluation of an in vitro sulphidoleukotriene release test for diagnosis of insect bite hypersensitivity in horses

REASONS FOR PERFORMING STUDY

Insect bite hypersensitivity (IBH) is an IgE-mediated allergic dermatitis caused by bites of Culicoides and Simulium species, and improved means of diagnosis are required.

OBJECTIVES

The cellular antigen simulation test (CAST) with C. nubeculosus and S. vittatum extracts was assessed in a population of IBH-affected and healthy horses. Variations in test results over a one year period and possible cross-reactivity between different insect extracts was studied.

METHODS

A total of 314 mature horses were studied using the CAST. Influence of severity of clinical signs, gender and age were evaluated, and 32 horses were tested repeatedly over one year. The kappa reliability test was used to assess agreement of the test results with different insect extracts.

RESULTS

Horses with IBH had significantly higher sLT release than controls with C. nubeculosus and S. vittatum. The highest diagnostic sensitivity and specificity levels were attained when using adult C. nubeculosus extracts with the CAST (78% and 97%, respectively), suggesting that most horses with IBH are sensitised against Culicoides allergens. A proportion of IBH-affected horses was found to be sensitised to allergens of Simulium spp. in addition to those of C. nubeculosus. The CAST with C. nubeculosus had positive and negative predictive values > or = 80% for a true prevalence of IBH of 12-52%. In the follow-up study, the proportion of IBH-affected horses with a positive test result ranged from 90% in November to 68% in March. Severity of clinical signs or age did not influence test results significantly. However, IBH-affected males achieved significantly more positive test results than IBH-affected females.

CONCLUSIONS

The CAST with adult C. nubeculosus has high specificity and good sensitivity for diagnosis of IBH. Horses with IBH are mainly sensitised to Culicoides allergens, and some horses are additionally also sensitised to allergens in Simulium spp.

POTENTIAL RELEVANCE

The CAST is likely to be a useful test for diagnosis of IBH, even allowing the identification of IBH-affected but asymptomatic horses. This test may also help in further characterisation of allergens involved in this condition.

Identification and isolation of cDNA clones encoding the abundant secreted proteins in the saliva proteome of Culicoides nubeculosus

Culicoides spp. are vectors of several infectious diseases of veterinary importance and a major cause of allergy in horses and other livestock. Their saliva contains a number of proteins which enable blood feeding, enhance disease transmission and act as allergens. We report the construction of a novel cDNA library from Culicoides nubeculosus linked to the analysis of abundant salivary gland proteins by mass spectrometry. Fifty-four novel proteins sequences are described including those of the enzymes maltase, hyaluronidase and two serine proteases demonstrated to be present in Culicoides salivary glands, as well as several members of the D7 family and protease inhibitors with putative anticoagulant activity. In addition, several families of abundant proteins with unknown function were identified including some of the major candidate allergens that cause insect bite hypersensitivity in horses.

Mucosal immunization against ovine lentivirus using PEI-DNA complexes and modified vaccinia Ankara encoding the gag and/or env genes

Sheep were immunized against Visna/Maedi virus (VMV) gag and/or env genes via the nasopharynx-associated lymphoid tissue (NALT) and lung using polyethylenimine (PEI)-DNA complexes and modified vaccinia Ankara, and challenged with live virus via the lung. env immunization enhanced humoral responses prior to but not after VMV challenge. Systemic T cell proliferative and cytotoxic responses were generally low, with the responses following single gag gene immunization being significantly depressed after challenge. A transient reduction in provirus load in the blood early after challenge was observed following env immunization, whilst the gag gene either alone or in combination with env resulted in significantly elevated provirus loads in lung. However, despite this, a significant reduction in lesion score was observed in animals immunized with the single gag gene at post-mortem. Inclusion of IFN-gamma in the immunization mixture in general had no significant effects. The results thus showed that protective effects against VMV-induced lesions can be induced following respiratory immunization with the single gag gene, though this was accompanied by an increased pulmonary provirus load.

Immune response to maedi-visna virus

The ovine maedi-visna virus (MVV) was the first lentivirus to be isolated and characterized 1957 in Iceland. MVV leads to a life-long, persistent infection with slow development of lesions in the lung and the central nervous system (CNS). The main target cells of MVV are of the monocyte/macrophage lineage and it does not infect T-lymphocytes or cause immune suppression like human immune deficiency virus (HIV). In spite of a fairly good immune response, including both neutralizing antibodies and cytotoxic T lymphocytes, the virus persists in the host and establishes a life-long infection. There are strong indications that the pathological lesions are immune-mediated and vaccination attempts have not only failed to induce sterile immunity but have occasionally caused increased viremia and more severe disease.

Equine insect bite hypersensitivity: immunoblot analysis of IgE and IgG subclass responses to Culicoides nubeculosus salivary gland extract

Insect bite hypersensitivity (IBH) is an allergic dermatitis of horses caused by IgE-mediated reactions to bites of Culicoides and sometimes Simulium spp. The allergens causing IBH are probably salivary gland proteins from these insects, but they have not yet been identified. The aim of our study was to identify the number and molecular weight of salivary gland extract (SGE) proteins derived from Culicoides nubeculosus which are able to bind IgE antibodies (ab) from the sera of IBH-affected horses. Additionally, we sought to investigate the IgG subclass (IgGa, IgGb and IgGT) reactivity to these proteins. Individual IgE and IgG subclass responses to proteins of C. nubeculosus SGE were evaluated by immunoblot in 42 IBH-affected and 26 healthy horses belonging to different groups (Icelandic horses born in Iceland, Icelandic horses and horses from different breeds born in mainland Europe). Additionally, the specific antibody response was studied before exposure to bites of Culicoides spp. and over a period of 3 years in a cohort of 10 Icelandic horses born in Iceland and imported to Switzerland. Ten IgE-binding protein bands with approximate molecular weights of 75, 66, 52, 48, 47, 32, 22/21, 19, 15, 13/12 kDa were found in the SGE. Five of these bands bound IgE from 50% or more of the horse sera. Thirty-nine of the 42 IBH-affected horses but only 2 of the 26 healthy horses showed IgE-binding to the SGE (p<0.000001). Similarly, more IBH-affected than healthy horses had IgGa ab binding to the Culicoides SGE (19/22 and 9/22, respectively, p<0.01). Sera of IBH-affected horses contained IgE, IgGa and IgGT but not IgGb ab against significantly more protein bands than the sera of the healthy horses. The cohort of 10 Icelandic horses confirmed these results and showed that Culicoides SGE specific IgE correlates with onset of IBH. IBH-affected horses that were born in Iceland had IgGa and IgGT ab (p< or =0.01) as well as IgE ab (p=0.06) against a significantly higher number of SGE proteins than IBH-affected horses born in mainland Europe. The present study shows that Culicoides SGE contains at least 10 potential allergens for IBH and that IBH-affected horses show a large variety of IgE-binding patterns in immunoblots. These findings are important for the future development of a specific immunotherapy with recombinant salivary gland allergens.

Diagnostic tests for small ruminant lentiviruses

Maedi visna virus and caprine arthritis encephalitis virus are closely related retroviruses that cause chronic inflammatory disease in small ruminants. The infections are characterised by insidious onset and slow progression. Diagnosis of infection is usually by serological testing. A variety of assays are available for this purpose, though the relative sensitivity and specificity of these assays has not been compared systematically. Here we review recent developments in laboratory diagnostic methods and their use in field diagnosis. The results suggest that a combination of ELISA and PCR might afford optimal detection of SRLV infection.

Transmission of small ruminant lentiviruses

Small ruminant lentiviruses (SRLV) are classical slow retroviruses causing chronic inflammatory disease in a variety of target organs. The routes of transmission have been investigated and a large body of evidence has accumulated over many years. The main routes are through ingestion of infected colostrum and/or milk, or through inhalation of respiratory secretions. However, many studies also provide evidence that intrauterine infection may occur, though the extent and significance of this route is controversial. Embryos treated to IETS standards appear to pose very little risk of infection. SRLV have been detected in semen suggesting a potential source of transmission. However, such transmission has not been demonstrated to date. The application of control measures based on this information allows more efficient strategies to be developed which will reduce the rate of transmission.

Cloning and sequencing of a cDNA expressing a ribosomal P0 peptide from Culicoides nubeculosus (Diptera)

Insect bite dermal hypersensitivity (IBH) is an allergic dermatitis of horses caused by bites of Culicoides spp. and sometimes Simulium spp. The aim of the investigation presented here was to identify allergens causing IBH. A cDNA library expressing recombinant Culicoides nubeculosus proteins was screened using affinity-purified serum from an IBH-affected horse. Screening of the library resulted in identification of one immunoreactive clone. The sequence of the cDNA insert was determined and revealed a 600 bp insert with an open reading frame coding for a 78 amino acid long protein, called rCul n 1. Analysis of the deduced amino acid sequence revealed an identity of 67-78% to the C-terminal part of the 318 amino acid long ribosomal P0 protein from other Diptera. Furthermore, the 38 C-terminal amino acids displayed an identity of 57% with the C-terminal part of the acidic ribosomal protein P2 from Aspergillus fumigatus. The cDNA insert was subcloned and expressed as a [His]6-tagged protein in Escherichia coli and purified using Ni2(+)-chelate affinity chromatography. The 10kDa recombinant Cul n 1 protein bound the affinity-purified antibody fraction used for screening the expression library. Determination of IgE and IgG levels against rCul n 1 by ELISA in sera from 19 IBH-affected and 18 Swiss control horses and in sera from eight control horses living in Iceland showed no significant differences between the three groups of horses (median IgE levels = 60, 49 and 44 relative ELISA units, respectively). rCul n 1 did not induce sulfidoleukotriene (sLT) release from peripheral blood leukocytes of IBH-affected horses (N = 5), although sLT release was induced with the Culicoides whole body extract.

Mimicry of a 21.5 kDa myelin basic protein peptide by a Maedi Visna virus polymerase peptide does not contribute to the pathogenesis of encephalitis in sheep

Epitope mimicry is the theory that an infectious agent such as a virus causes pathological effects via mimicry of host proteins and thus elicits a cross-reactive immune response to host tissues. Weise and Carnegie (1988) found a region of sequence similarity between the pol gene of the Maedi Visna virus (MVV), which induces demyelinating encephalitis in sheep, and myelin basic protein (MBP), which is known to induce experimental allergic encephalitis (EAE) in laboratory animals. In this study, cross-reactions between sera raised in sheep against synthetic peptides of MVV (TGKIPWILLPGR) and 21.5 kDa MBP (SGKVPWLKPGR) were demonstrated using enzyme-linked immunosorbant assay (ELISA) and thin layer chromatography (TLC) immunoprobing. The antibody responses of MVV-infected sheep were investigated using ELISA against the peptides, and MBP protein, immunoprobing of the peptides on TLC plates and Western blotting against MBP. Slight significant reactions to the 21.5 kDa MBP peptide (P < 0.001) and to a lesser extent sheep MBP (P < 0.004) were detected in ELISA. The MBP peptide evoked stronger responses from more sera than the MVV peptide on immunoprobed TLC plates. On the Western blots, eight of the 23 sheep with Visna had serum reactivity to MBP. This slight reaction to MBP in MVV-infected sheep is of interest because of the immune responses to MBP evident in multiple sclerosis and EAE, but its relevance in Visna is limited since no correlation with disease severity was observed. The cell-mediated immune responses of MVV-infected sheep against similar peptides was assessed. The peptides did not stimulate proliferation of peripheral blood lymphocytes of MVV-infected sheep. Since the MVV peptide was not recognised by antibodies or T lymphocytes from MVV-infected and encephalic sheep, it was concluded that epitope mimicry of this 21.5 kDa MBP peptide by the similar MVV pol peptide was not contributing to the immunopathogensis of Visna. The slight antibody response to MBP and the MBP peptide can be attributed to by-stander effects of the immunopathology of MVV-induced encephalitis.

Over-expression of C-myc increases the sensitivity of Epstein-Barr virus immortalized lymphoblastoid cells to non-MHC-restricted cytotoxicity

Epstein-Barr virus (EBV)-carrying Burkitt lymphoma (BL) lines which maintain the phenotypic characteristics of the in vivo tumor cells are more sensitive to natural (NK), interferon-activated (IAK) and IL-2-activated (LAK) cytotoxicity than EBV-immortalized lymphoblastoid cell lines (LCL) of normal B-cell origin. All BL cells carry chromosomal translocations which lead to deregulated expression of the c-myc oncogene. LCLs transfected with constitutively active c-myc alleles display changes in growth properties and surface phenotype. In this study, we have examined the effect of c-myc deregulation on the sensitivity of LCLs to NK, IAK and LAK effectors. C-myc-transfected LCLs showed an increased sensitivity to lysis which correlated with the level of c-myc expression. Expression of HLA class I and sensitivity to allospecific and EBV-specific cytotoxic T-lymphocytes (CTL) remained unchanged. Transfection of a constitutively active v-H-ras gene, which also induces changes in growth properties and cell-surface phenotype, did not alter the sensitivity of LCLs to NK or LAK cytotoxicity.

Stimulation with allogeneic Epstein-Barr virus-transformed lymphoblastoid cell lines generates HLA class I-specific CTLs with different target cell avidity

Epstein-Barr virus (EBV) transformed lymphoblastoid cell lines (LCL) are potent inducers of cytotoxic T-lymphocytes (CTL) in allogeneic mixed lymphocyte cultures (MLC). The contribution of EBV antigens to the induction of cytotoxic responses was investigated by comparing CTL clones derived from allogeneic MLCs of lymphocytes from one EBV seropositive and one seronegative donor for their capacity to lyse paired EBV positive and negative targets. The majority of the clones showed a conventional "HLA-specific" cytotoxicity and lysed equally well HLA-matched LCLs and mitogen-induced T- or B-blasts. A minority of the clones from both donors exhibited an "LCL-selective" killing potential as they lysed poorly T- and B-blasts. The LCL-selective clones did not recognize EBV antigens because they could not discriminate between EBV negative Burkitt lymphoma (BL) lines and their in vitro EBV-converted sublines. MAbs to CD3, CD8, and MHC class I antigens blocked the lysis of LCLs by HLA-specific and LCL-selective CTLs with comparable efficiency suggesting that the two effector types express T-cell receptors of similar affinity. T-blasts were unable to inhibit the lysis of LCLs in cross competition assays. This correlated with a significantly lower expression of the cell adhesion molecules ICAM-1 and LFA-3. The results suggest that stimulation with allogeneic LCLs activates HLA class I-specific CTLs with variable target cell avidity. Only CTLs that act independently of the enhancing effect of cell adhesion molecules are able to lyse mitogen-induced T- and B-blasts.

Search for the critical characteristics of phenotypically different B cell lines, Burkitt lymphoma cells and lymphoblastoid cell lines, which determine differences in their functional interaction with allogeneic lymphocytes

Burkitt lymphoma (BL) lines can be grouped according to phenotypic characteristics. Group I cells exhibit the phenotype of resting B cells and grow as single cells. Such lines can be Epstein-Barr-virus(EBV)-negative or -positive. Group II and group III cells are always EBV-positive, they express B cell activation markers, grow in aggregates and resemble in varying degrees lymphoblastoid cell lines (LCL). We studied three groups of BL lines for their capacity to interact with allogeneic lymphocytes. The results showed that as long as the lines have the group I phenotype, they do not stimulate allogeneic T lymphocytes irrespective whether they carry the EBV genome. The group II and III cells are stimulatory. Generally there was no correlation between sensitivity ot lymphocyte-mediated lysis and the phenotype of the lines. In one set of lines, the group I cells had higher sensitivity to both natural killer and lymphokine-activated killer effectors compared to the group II or III lines. However, such correlation could not be seen with the other two sets of lines. Among the phenotypic features investigated, expression of the adhesion molecules LFA-1 and LFA-3 correlated with the tendency for cell aggregation.

Studies of sublines selected for loss of HLA expression from an EBV-transformed lymphoblastoid cell line. Changes in sensitivity to cytotoxic T cells activated by allostimulation and natural killer cells activated by IFN or IL-2

Murine tumor studies have suggested that variations in MHC class I expression may influence the behavior of tumor cells in vivo. Corresponding human tumor studies remain at the descriptive level but they show differences in MHC Ag expression between and even within tumors. Our purpose was to explore possible functional relationships between class I expression and sensitivity to different forms of cell-mediated lysis in a potentially immunogenic system: EBV-immortalized B cells. Their cytotoxic sensitivity was tested to CTL and to IFN- or IL-2-activated effector cells. The wild-type line (high class I) was sensitive to CTL with the appropriate Ag restriction, but resisted lysis by normal or IFN-activated PBL. In contrast, HLA loss variants showed a reduced sensitivity to CTL and an increased NK sensitivity. The latter could be related to the loss of class I molecules: an intermediate (haplotype loss) expressor variant was moderately NK sensitive, whereas a weak expressor line, with an additional down-regulation of the remaining haplotype, was highly sensitive. IL-2-activated PBL ("LAK") cells showed the same killing pattern as NK cells, although the levels of lysis were generally higher. These data support the hypothesis that the MHC class I Ag expression-dependent, CTL-mediated lysis is complemented by additional mechanisms, mediated by effectors that recognize cells with reduced MHC Ag expression that would otherwise escape CTL-mediated rejection.

Studies of sublines selected for loss of HLA expression from an EBV-transformed lymphoblastoid cell line. Changes in sensitivity to cytotoxic T cells activated by allostimulation and natural killer cells activated by IFN or IL-2

Murine tumor studies have suggested that variations in MHC class I expression may influence the behavior of tumor cells in vivo. Corresponding human tumor studies remain at the descriptive level but they show differences in MHC Ag expression between and even within tumors. Our purpose was to explore possible functional relationships between class I expression and sensitivity to different forms of cell-mediated lysis in a potentially immunogenic system: EBV-immortalized B cells. Their cytotoxic sensitivity was tested to CTL and to IFN- or IL-2-activated effector cells. The wild-type line (high class I) was sensitive to CTL with the appropriate Ag restriction, but resisted lysis by normal or IFN-activated PBL. In contrast, HLA loss variants showed a reduced sensitivity to CTL and an increased NK sensitivity. The latter could be related to the loss of class I molecules: an intermediate (haplotype loss) expressor variant was moderately NK sensitive, whereas a weak expressor line, with an additional down-regulation of the remaining haplotype, was highly sensitive. IL-2-activated PBL ("LAK") cells showed the same killing pattern as NK cells, although the levels of lysis were generally higher. These data support the hypothesis that the MHC class I Ag expression-dependent, CTL-mediated lysis is complemented by additional mechanisms, mediated by effectors that recognize cells with reduced MHC Ag expression that would otherwise escape CTL-mediated rejection.

Allele-specific down-regulation of MHC class I antigens in Burkitt lymphoma lines

We have reported that Burkitt lymphomas (BL) that arise in HLA-A11 positive individuals are resistant to lysis by HLA-A11-specific and HLA-A11-restricted CTLs(10,11). Here we show that this phenomenon can be explained by a selective loss of the HLA-A11 polypeptide. The HLA-A11 negative phenotype is due to a regulatory phenomenon, rather than a structural defect, as proven by the ability to rescue expression of HLA-A11 in in vitro Epstein-Barr virus (EBV)-converted sublines of EBV negative BLs.

Combined treatment with interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha up-regulates the expression of HLA class I determinants in Burkitt lymphoma lines

Cell lines derived from Epstein-Barr virus (EBV)-positive and EBV-negative Burkitt lymphoma (BL) have a low or defective expression of polymorphic HLA class I determinants compared to EBV-transformed lymphoblastoid cell lines (LCL) of normal B cell origin and are resistant to lysis by cytotoxic T lymphocytes (CTL) specific for the corresponding determinants (M. G. Masucci, S. Torsteinsdottir, J. Colombani, C. Brautbar, E. Klein, and G. Klein, Proc. Natl. Acad. Sci. USA 84, 4567, 1987; S. Torsteinsdottir, C. Brautbar, E. Klein, G. Klein, and M. G. Masucci, Int. J. Cancer, 41, 913, 1988). In order to investigate whether this phenotypic trait of the tumor cells can be modulated by agents known to enhance HLA class I antigen expression, pairs of LCL and BL lines were cultured in the presence of recombinant human interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha. Three low HLA A11 expressor EBV-negative BL lines, DG 75, BL 28, and BL 41, reacted significantly stronger with the anti-HLA A11 monoclonal antibody (Mab) AUF 5.13 after combined treatment with 500 U/ml IFN-gamma and 500 U/ml TNF-alpha. Reactivity with the AUF 5.13 and with other anti-polymorphic class I Mab's was up-regulated also in in vitro EBV-converted sublines of BL 28 and BL 41. The increment of antigen expression depended on the baseline expression in untreated cells. It was largest for the low expressor lines and decreased proportionally to the level of up-regulation induced by EBV conversion. Up-regulation of HLA A11 was accompanied by induction of sensitivity to HLA A11-specific CTLs in BL 28 and its converted subline E95A BL28 while BL 41 and E95A BL 41 remained resistant. The treatment did not affect significantly HLA A11 expression of two EBV-carrying, low HLA A11 expressor BL lines, WW-1-BL and WW-2-BL, and of the EBV-carrying BL 72 line that had a high spontaneous expression. The results suggest that the down-regulation of class I antigen expression is reversible in some but not all BL lines.

Differential expression of HLA antigens on human B-cell lines of normal and malignant origin: a consequence of immune surveillance or a phenotypic vestige of the progenitor cells?

Pairs of BL-derived cell lines and in vitro EBV-transformed LCLs, derived from the same patient, were compared for the expression of MHC class-I antigenic determinants as shown both by monoclonal antibody (MAb) binding and by sensitivity to HLA-specific CTL clones. BL lines expressed all polymorphic determinants tested at a lower level than the corresponding LCLs, as indicated by the binding of the MAbs AUF 5.13 (anti-HLA A3,A11), GS 142.1 (anti-HLA A1), GS 114.1 (anti-HLA A24), GSP 35.1 (anti-HLA A2,A28), GSP 55.1 (anti-HLA A25,A32), TER MA32 (anti-HLA A32), GSP 145.2 (anti-HLA B27), B27 M.1 (anti-HLA B27,B7) and GSP 8.1 (anti-HLA B8). The difference was most pronounced for HLA A11 and least for B27,A1 and B8 with intermediate differences for the other specificities. The BL lines were also less sensitive to lysis by HLA-specific CTL clones directed to the same and to additional antigens. The polymorphic determinants detected by the AUF 5.13 and GSP 35.1. MAbs were expressed at a lower level in resting T and B cells compared to mitogen- and EBV-induced blasts. An analogous change in the expression of polymorphic determinants was observed in EBV-converted sublines of originally EBV-negative BLs that have become more "LCL-like" after conversion. The appearance of B-cell activation markers was paralleled by the up-regulation of both the serologically defined and the CTL-target epitopes. The findings suggest that the low expression of HLA determinants on the BL cells is a phenotypic vestige of the normal BL precursor.

Paired Epstein-Barr virus (EBV)-negative and EBV-converted Burkitt lymphoma lines: stimulatory capacity in allogeneic mixed lymphocyte cultures

Epstein-Barr virus (EBV)-negative Burkitt lymphoma lines (BLE-) and their in vitro EBV-converted sublines (BLEc), obtained by infection with the P3HRI and B95-8 strains of EBV, were compared for their capacity to induce T-lymphocyte proliferation in allogeneic mixed lymphocyte cultures (MLC). Regardless of the virus strain used for conversion, the BLEc lines induced a considerably stronger primary MLC response than their EBV-negative parentals. Only the BLEc lines were able to maintain T-lymphocyte proliferation in repeated stimulations. The low proliferative response observed in cultures stimulated with BLE- cells was not due to the generation of suppressor cells or to the release of inhibitory factors. The increased stimulatory capacity of BLEc lines was unrelated to changes in expression of MHC class-I and class-II antigen, or of B-cell activation markers, and was not due to the reactivation of EBV-specific memory T cells, since lymphocytes from EBV-seropositive and seronegative donors responded similarly. The results indicate that the capacity of BL cells to elicit cellular immune responses may be influenced by their EBV-carrying status.

Activation of B lymphocytes by Epstein-Barr virus/CR2 receptor interaction

Epstein-Barr virus (EBV) infects and transforms human B lymphocytes. The virus receptor was shown to be identical to the complement receptor CR2. The consequences of EBV/CR2 receptor interaction on B lymphocyte activation were analyzed by infection of B cells with the transforming (B95-8) and the nontransforming (P3HR1) virus strains and with UV-inactivated B95-8 virus. Similar to mitogens and antibodies against surface IgM and CR2 receptor, transforming and nontransforming EBV induced the release of leukocyte migration inhibitory factor (LIF). LIF production occurred early after infection and was not affected by irradiation of the B95-8 virus with doses of UV-light which prevented the expression of viral functions. B lymphocytes infected with UV-inactivated virus responded to T cell-derived B cell growth factors. The results demonstrate that binding of EBV to the CR2 receptor activates the B cells. Progression of the infected cells in the activation pathway required helper cell-derived factors or signals provided by the intact viral genome. The nontransforming P3HR1 virus induced a low level of RNA synthesis and increase of cell size and major histocompatibility complex class I antigen expression. Only the transforming virus induced expression of EBV nuclear antigens and cellular DNA synthesis.

Differentiation-dependent sensitivity of human B-cell-derived lines to major histocompatibility complex-restricted T-cell cytotoxicity

Sets of Burkitt lymphoma lines and Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines (LCLs) derived from the same individuals were compared for sensitivity to cytotoxic T-lymphocyte (CTL) clones. Major histocompatibility complex class I antigen-restricted CTL clones were generated by stimulating the lymphocytes of an EBV-seropositive individual with the autologous LCL. One clone (BK-20) lysed the autologous and allogeneic HLA-A11-expressing LCLs but not mitogen-induced B lymphoblasts. Thus the clone was selectively cytotoxic for LCLs. Allospecific CTL clones directed against the HLA-A11 antigen were generated from an EBV-seronegative individual. One clone (WP-36) was selectively cytotoxic for the appropriate allospecific LCL, whereas another clone (WP-21) lysed also T and B lymphoblasts. None of the four Burkitt lymphoma lines established in parallel with the CTL-sensitive LCLs were lysed. Two of the Burkitt lymphoma lines were EBV-negative, and EBV-positive sublines were derived from these by in vitro infection. One but not the other of the two convertants became sensitive to all three types of CTL clones. The CTL-sensitive converted line had also acquired some LCL characteristics: increased cell size, aggregation, and a shift in several of the B-cell-specific surface markers. The CTL-resistant convertant expressed EBV antigens but showed no phenotypic change. These findings suggest that the cellular phenotype plays a decisive role in the sensitivity of B-cell-derived lines to the lytic effect of LCL-selective autologous and allogeneic CTLs.

Differential recognition of tumor-derived and in vitro Epstein-Barr virus-transformed B-cell lines by fetal calf serum-specific T4-positive cytotoxic T-lymphocyte clones

Two interleukin-2 (IL-2)-dependent cytotoxic T-cell clones were obtained by limiting dilution from a lymphocyte culture stimulated in vitro with the autologous Epstein-Barr virus-transformed lymphoblastoid cell line (LCL) in the presence of fetal calf serum (FCS). Both clones uniformly had a T3+, T4+, Dr+ phenotype and lysed autologous B blasts, the autologous LCL, and allogeneic B cell lines sharing major histocompatibility complex (MHC) class II antigens. The cytotoxic function was triggered by FCS-derived components. There was no killing if the sensitive targets were cultured in serum-free medium or in medium supplemented with human serum. Sensitivity to lysis could be restored by exposing the targets to FCS for at least 6 hr at 37 degrees C. Monoclonal antibodies directed to T-cell-specific surface antigens and MHC class II antigens inhibited lysis with different efficiencies depending on the target cell origin. Killing of Burkitt's lymphoma (BL)-derived cell lines was blocked more easily than killing of LCLs. LCLs but not BL lines induced proliferation of the T-cell clones in the absence of exogenous IL-2. The differences were not related to quantitative variations in the expression of MHC class II antigens, indicating that BL lines differ from LCLs in other cell membrane properties that may influence antigen presentation. The results suggest that the affinity of effector/target binding, which is probably influenced by the concentration of antigenic determinants expressed on the target cell membrane, determines whether proliferative responses or cytotoxicity are induced in the antigen-recognizing T cells.

Selective inhibitory effect of Hu-IFN-gamma on the agarose clonability of tumor-derived lymphoid cell lines

Recombinant human interferon alpha (IFN-alpha) and interferon gamma (IFN-gamma) were compared for their ability to influence the proliferative capacity of tumor-derived cell lines and of normal B lymphocytes infected in vitro by Epstein-Barr virus (EBV). EBV-induced B-cell proliferation was suppressed almost completely when 10(2) U/ml IFN-alpha were added to the culture medium while the same dose of IFN-gamma had significantly lower inhibitory activity. The pure IFNs differed in their ability to influence the growth of three Burkitt lymphoma-derived cell lines, Raji, Daudi, and Namalwa, depending on whether the cells were propagated in suspension or in semisolid cultures. IFN-alpha inhibited cell proliferation under both culture conditions with thresholds of sensitivity characteristics for each cell line. In contrast, IFN-gamma had no effect on the growth in suspension but it abolished the clonogenic potential of tumor cell lines in semisolid agarose. The results suggest that the two IFN types may exert their growth inhibitory activity through different mechanisms of action.

Phorbol esters inhibit the functional activation of cytotoxic precursors in mixed lymphocyte cultures

We have investigated the effect of phorbol esters on T cell activation and generation of suppressor and cytotoxic activity in mixed lymphocyte cultures (MLC). The presence of 30 nM P(Bu)2 during the sensitization phase inhibited the generation of allospecific cytotoxicity and also decreased the killing potential against NK-sensitive targets. The inhibition was not mediated by direct blocking of the lytic capacity nor by suppression of clonal expansion of cytotoxic cells through modulation of lymphokine production. The presence of P(Bu)2 enhanced cell proliferation, but inhibited the functional activation of lymphocytes and consequent generation of Dr antigen-positive T cells. Because the presence of the compound did not affect the MLC-induced generation of suppressor activity, it is likely that P(Bu)2 selectively blocks the maturation of cytotoxic precursors. Surface-marker analysis with OKT monoclonal antibodies revealed that the effects on lymphocyte activation were associated with a decrease in OKT3 and OKT4 reactivity and an increase in the percentage of OKT8-positive cells. The decrease in OKT4 reactivity was not due to selective loss of this lymphocyte subpopulation, because P(Bu)2 was equally mitogenic for the purified OKT4- and OKT8-positive subsets. The results suggest that the effect of P(Bu)2 on cell differentiation and its ability to modulate the expression of functional markers in lymphocyte subsets may interfere with T-T cell cooperation that controls the functional maturation of cytotoxic precursors.

Phorbol esters inhibit the functional activation of cytotoxic precursors in mixed lymphocyte cultures

We have investigated the effect of phorbol esters on T cell activation and generation of suppressor and cytotoxic activity in mixed lymphocyte cultures (MLC). The presence of 30 nM P(Bu)2 during the sensitization phase inhibited the generation of allospecific cytotoxicity and also decreased the killing potential against NK-sensitive targets. The inhibition was not mediated by direct blocking of the lytic capacity nor by suppression of clonal expansion of cytotoxic cells through modulation of lymphokine production. The presence of P(Bu)2 enhanced cell proliferation, but inhibited the functional activation of lymphocytes and consequent generation of Dr antigen-positive T cells. Because the presence of the compound did not affect the MLC-induced generation of suppressor activity, it is likely that P(Bu)2 selectively blocks the maturation of cytotoxic precursors. Surface-marker analysis with OKT monoclonal antibodies revealed that the effects on lymphocyte activation were associated with a decrease in OKT3 and OKT4 reactivity and an increase in the percentage of OKT8-positive cells. The decrease in OKT4 reactivity was not due to selective loss of this lymphocyte subpopulation, because P(Bu)2 was equally mitogenic for the purified OKT4- and OKT8-positive subsets. The results suggest that the effect of P(Bu)2 on cell differentiation and its ability to modulate the expression of functional markers in lymphocyte subsets may interfere with T-T cell cooperation that controls the functional maturation of cytotoxic precursors.

T lymphocyte culture established by repeated stimulation with the autologous lymphoblastoid line. MHC class II restricted interactions with B blasts

An OKT3+T4+T8-DR+ lymphocyte line was developed from an Epstein-Barr virus (EBV) seropositive individual by repeated stimulation in vitro with autologous EBV-infected B cells. The T cell population designated E-44 was carried for eight months in the presence of Interleukin-2 and was repeatedly tested for cytotoxicity, proliferation and lymphokine production in response to the autologous and a panel of allogenic B cells. The E-44 cells lysed the autologous lymphoblastoid cell lines (LCL) and allogenic B cell lines sharing the DR6.1 major histocompatibility complex antigen with the lymphocyte donors. The EBV genome-negative lymphoma line BJAB and its two, infected in vitro, EBV-positive sublines were lysed with similar efficiencies. Autologous Staphylococcus aureus protein A (Prot-A) induced B, but not Phytohaemagglutinin (PHA)-induced T blasts were also lysed. It is likely that E-44 recognized an antigenic component derived from the fetal calf serum in association with class II determinants expressed on the B cells. Preincubation of E-44 cells with saturating amounts of OKT3 and Leu3a monoclonal antibodies abrogated the lytic effect on the autologous LCL. Cold target competition experiments demonstrated that, within, the population, the same cells reacted with the autologous Prot-A-induced blasts, the EBV-transformed LCL, and also with Daudi (an EBV genome-positive BL line). Although Daudi was the target which was lysed with the greatest efficiency, the avidity of interaction was highest with the autologous LCL because these cells competed best. Among the cells that were sensitive for the lytic effect, only the autologous LCL and Prot-A-induced B blasts triggered release of detectable amounts of Interleukin-2 and induced proliferation of the culture. The results suggest that the affinity of interaction with the target may be decisive for the triggering of the various T cell functions.

Natural killer cell sensitivity of human lymphoid lines of B-cell origin does not correlate with tumorigenicity or with the expression of certain differentiation markers

Human B-cell lines derived from normal donors (LCL) or from Burkitt lymphomas (BL) were compared for their sensitivity to natural (NK) and interferon (IFN)-activated (IAK) cytotoxicity, mediated by effector cells from normal human blood. In four cases, a BL and an LCL line were derived from the same donor and had been kept in culture for the same period of time. The BL series included both Epstein-Barr virus (EBV)-carrying and EBV-negative lymphoma lines. The latter were compared with their own EBV-converted, Epstein-Barr nuclear antigen (EBNA)- and EBV-DNA-positive sublines, established by in vitro infection with two different viral substrains. LCL and BL lines from the same donor were lysed with equal efficiency by both NK and IAK effectors. There was no relationship between the NK sensitivity and the nude mouse tumorigenicity of different EBV-converted Ramos sublines, or the expression of differentiation markers such as insulin receptor, surface IgD, and the B2 surface antigen. Moreover, EBV-converted sublines of BJAB differed in their NK sensitivity, in spite of closely similar expression of these markers. NK-sensitive Ramos and BJAB sublines induced a stronger proliferative response upon confrontation with allogeneic lymphocytes than their NK-resistant counterparts. This suggests that the target cell may play an active role in triggering the lytic interaction. There was no correlation between this property and any of the other parameters studied.