Autoantibodies to Annexin A2 and cerebral thrombosis: Insights from a mouse model.

INTRODUCTION: Antiphospholipid syndrome (APS) is an autoimmune disorder manifested by thromboembolic events, recurrent spontaneous abortions and elevated titers of circulating antiphospholipid antibodies. In addition, the presence of antiphospholipid antibodies seems to confer a fivefold higher risk for stroke or transient ischemic attack. Although the major antigen of APS is ß2 glycoprotein I, it is now well established that antiphospholipid antibodies are heterogeneous and bind to various targets. Recently, antibodies to Annexin A2 (ANXA2) have been reported in APS. This is of special interest since data indicated ANXA2 as a key player in fibrinolysis. Therefore, in the present study we assessed whether anti-ANXA2 antibodies play a pathological role in thrombosis associated disease. MATERIALS AND METHODS: Mice were induced to produce anti-ANXA2 antibodies by immunization with ANXA2 (iANXA2) and control mice were immunized with adjuvant only. A middle cerebral artery occlusion stroke model was applied to the mice. The outcome of stroke severity was assessed and compared between the two groups. RESULTS: Our results indicate that antibodies to ANXA2 lead to a more severe stroke as demonstrated by a significant larger stroke infarct volume (iANXA2 133.9 ± 3.3 mm3 and control 113.7 ± 7.4 mm3; p = 0.017) and a more severe neurological outcome (iANXA2 2.2 ± 0.2, and control 1.5 ± 0.18; p = 0.03). CONCLUSIONS: This study supports the hypothesis that auto-antibodies to ANXA2 are an independent risk factor for cerebral thrombosis. Consequently, we propose screening for anti-ANXA2 antibodies should be more widely used and patients that exhibit the manifestations of APS should be closely monitored by physicians.

Mimotope-based antigens as potential vaccine candidates in experimental murine cysticercosis.

Human cysticercosis is a public health problem caused by Taenia solium metacestodes; thus, eradication of T. solium transmission by vaccination is an urgent requirement. The Cc48 mimotope from T. solium cysticerci was tested expressed in phage particles (mCc48) and chemically synthesized (sCc48) as a vaccine candidate in experimental murine cysticercosis. For this, BALB/c mice were immunized with mCc48 (G1; n = 40), sCc48 (G2; n = 40) and phosphate-buffered saline (PBS) (G3; n = 40, positive control) and challenged with Taenia crassiceps metacestodes. Another PBS group without parasite challenge was used as a negative control (G4; n = 40). Mice were sacrificed 15, 30, 45 and 60 days post-infection for cysticerci and serum collection. Immunization efficacy was determined by cysticerci counting. Serum samples were tested by ELISA to verify antibody (IgM, IgG, IgA and IgE) and cytokine (IFNγ and IL-4) levels. The sCc48 achieved the highest rates of protection and efficacy (90 and 98%, respectively). The group immunized with mCc48 presented the highest reactivity for IgM, IgG and IgE. All groups presented IL-4, but IFNγ was quite variable among groups. The protection induced by sCc48 synthetic peptide supports further studies of this mimotope as a potential vaccine candidate against cysticercosis.

Genetic regulation of antibody responsiveness to immunization in substrains of BALB/c mice.

Antibody-mediated immunity is highly protective against disease. The majority of current vaccines confer protection through humoral immunity, but there is high variability in responsiveness across populations. Identifying immune mechanisms that mediate low antibody responsiveness may provide potential strategies to boost vaccine efficacy. Here, we report diverse antibody responsiveness to unadjuvanted as well as adjuvanted immunization in substrains of BALB/c mice, resulting in high and low antibody response phenotypes. Furthermore, these antibody phenotypes were not affected by changes in environmental factors such as the gut microbiota composition. Antigen-specific B cells following immunization had a marked difference in capability to class switch, resulting in perturbed IgG isotype antibody production. In vitro, a B-cell intrinsic defect in the regulation of class-switch recombination was identified in mice with low IgG antibody production. Whole genome sequencing identified polymorphisms associated with the magnitude of antibody produced, and we propose candidate genes that may regulate isotype class-switching capability. This study highlights that mice sourced from different vendors can have significantly altered humoral immune response profiles, and provides a resource to interrogate genetic regulators of antibody responsiveness. Together these results further our understanding of immune heterogeneity and suggest additional research on the genetic influences of adjuvanted vaccine strategies is warranted for enhancing vaccine efficacy.

Induction of protective immunity by recombinant peptidoglycan associated lipoprotein (rPAL) protein of Legionella pneumophila in a BALB/c mouse model.

Legionella pneumophila causes a severe form of pneumonia known as Legionnaires' disease especially in patients with impaired cellular immune response. In order to prevent the disease, immunogenicity and the level of the induction of protective immunity from the recombinant peptidoglycan-associated lipoprotein (rPAL) against Legionella pneumophila in BALB/c mice was examined. Mice immunized with (rPAL) rapidly increased an antibody response in serum and also displayed a strong activation of both innate and adaptive cell-mediated immunity as determined by antigen-specific splenocyte proliferation, an early production of pro-inflammatory cytokines in the serum and in the splenocyte cultures. Infection with a primary sublethal does of Legionella pneumophila serogroup 1, strain paris, caused resistance to a lethal challenge infection in the animals with 100% survival rate. However, mice treated with rPAL survived with 60% rate in 10 days after a lethal i.v challenge with L. pneumophila. All of the control animals receiving PBS died within 24 h. The present study indicates that recombinant protein PAL of Legionella pneumophila is strongly immunogenic and capable to elicit early innate and adaptive immune responses and lasting immunity against a lethal dose of Legionella pneumophila challenge. Antigenic characterization and immune protection of recombinant protein PAL would be of considerable value in comprehension the immune-pathogenesis of the disease and in development possible vaccine against the Legionella.

Comparative Analysis of Bone Marrow-derived Mast Cell Differentiation in C57BL/6 and BALB/c Mice.

Allergic diseases have increased in the last three decades. Mast cells play a critical role in allergic diseases along with allergen-specific immunoglobulin E (IgE). Following mast cell degranulation elicited by ligation of the IgE-FcεRI receptor complex with allergen, allergic reactions are followed by various symptoms such as vascular hyperpermeability, mucous secretion, itching, sneezing, wheezing, rashes, fever, and anaphylactic shock. Susceptibility or inclination to allergy varies depending on individual genetic traits and living environment, and it has long been believed that such an inclination is determined by an immunologic balance of T helper cell types. Mouse strains also have different susceptibilities to allergy. Similar to T helper cells and macrophages, it is not known whether mast cells can also be divided into two different types between mouse strains. In this study, we prepared bone marrow-derived mast cells from BALB/c and C57BL/6 mice and examined their cellular properties. Cellular response to IL-3 and the process of mast cell differentiation from bone marrow cells were different on the basis of cell surface marker molecules. BALB/c-derived cells more efficiently exhibited degranulation than did C57BL/6-derived cells following both calcium ionophore and receptor crosslinking. These functional differences persisted even after a longer cell culture for 8 weeks, suggesting a difference in cell-autonomous characteristics. These results support the concept that mast cells also have different cell types dependent on their genetic background. Abbreviations: Ab: antibody; BMMC: bone marrow-derived mast cell; DNP: dinitrophenyl; FACS: fluorescence-activated cell sorter; FCS: fetal calf serum; FITC: fluorescein isothiocyanate; FSC: forward scatter; HRP: horseradish peroxidase; HSA: human serum albumin; Ig: immunoglobulin; IL: interleukin; MIP-2: macrophage inflammatory protein-2; MCP: mast cell protease; PE: phycoerythrin; PerCP: Peridinin chlorophyll protein complex; SNP: single nucleotide polymorphisms; SSC: side scatter; Th: T helper; TNF-α: tumor necrosis factor alpha.

A new immunochromatographic assay for on-site detection of porcine epidemic diarrhea virus based on monoclonal antibodies prepared by using cell surface fluorescence immunosorbent assay.

BACKGROUND: Porcine epidemic diarrhea virus (PEDV) is a highly effective pathogen that can cause death of new-born piglet, resulting in big economical loss in pig farming industry. For rapid detection of PEDV, a new immunochromatographic assay (ICA) based on monoclonal antibodies (mAbs) was developed in this study. RESULTS: The mAbs were prepared by using PEDV positive hybridoma cells that were selected by using cell surface fluorescence immunosorbent assay (CSFIA). Fourteen mAbs against PEDV strain isolated from south of China were prepared. The optimal mAb 4A11 was coated on NC membrane as the capturing reagent and the mAb A11H7 was coupled to gold nanoparticles (AuNPs) as detection reagent for the new ICA. The new ICA was used to measure PEDV in phosphate buffer containing tween-20. Results indicated that the limit of detection (LOD) of the new ICA was 0.47 µg/mL (5.9 × 103 TCID50/mL) and the liner detection range of the ICA was 0.625-10 µg/mL (7.8 × 103-105 TCID50/mL). The specificity analysis results showed that this new ICA had no cross reaction in the presence of other porcine viruses. The ICA was also validated for the detection of PEDV in swine stool samples with little interference from swine stool. To compare its accuracy to other traditional detection methods, 27 swine stool samples from south of China were investigated with the new developed ICA, commercial strip and RT-PCR. Results showed that the new ICA was more comparable to RT-PCR than commercial test strip. CONCLUSIONS: A new ICA based on mAbs prepared by CSFIA was developed in this study. It was a sensitive, specific and rapid method that could be used for on-site detection of PEDV and therefore was useful for the diagnosis and prevention of PED.

Rapid detection of cow milk adulteration/contamination in goat milk by a lateral flow colloidal gold immunoassay strip.

Current available methods to detect cow milk adulteration or accidental contamination of goat milk are both laborious and time consuming. The aim of this technical research communication was to develop a simple, rapid, specific and sensitive method for quantitative detection of cow milk in goat milk. A competitive lateral flow immunoassay (LFIA) strip was developed using a specific monoclonal antibody (mAb) labeled with colloidal gold nanoparticles (GNPs) for specifically binding to cow milk casein. The detection limit of this rapid detection was 0.07% of cow milk in goat milk, providing equal specificity and higher sensitivity when compared with a commercial enzyme-linked immunosorbent assay (ELISA). These result suggest that the established rapid GNPs-LFIA strip could be used for monitoring cow milk adulteration/contamination of goat milk.

Virulence of the Melioidosis Pathogen Burkholderia pseudomallei Requires the Oxidoreductase Membrane Protein DsbB.

The naturally antibiotic-resistant bacterium Burkholderia pseudomallei is the causative agent of melioidosis, a disease with stubbornly high mortality and a complex, protracted treatment regimen. The worldwide incidence of melioidosis is likely grossly underreported, though it is known to be highly endemic in northern Australia and Southeast Asia. Bacterial disulfide bond (DSB) proteins catalyze the oxidative folding and isomerization of disulfide bonds in substrate proteins. In the present study, we demonstrate that B. pseudomallei membrane protein disulfide bond protein B (BpsDsbB) forms a functional redox relay with the previously characterized virulence mediator B. pseudomallei disulfide bond protein A (BpsDsbA). Genomic analysis of diverse B. pseudomallei clinical isolates demonstrated that dsbB is a highly conserved core gene. Critically, we show that DsbB is required for virulence in B. pseudomallei A panel of B. pseudomalleidsbB deletion strains (K96243, 576, MSHR2511, MSHR0305b, and MSHR5858) were phenotypically diverse according to the results of in vitro assays that assess hallmarks of virulence. Irrespective of their in vitro virulence phenotypes, two deletion strains were attenuated in a BALB/c mouse model of infection. A crystal structure of a DsbB-derived peptide complexed with BpsDsbA provides the first molecular characterization of their interaction. This work contributes to our broader understanding of DSB redox biology and will support the design of antimicrobial drugs active against this important family of bacterial virulence targets.

Improved and adopted murine models to combat pulmonary aspergillosis.

The insufficient basic and clinical knowledge about invasive mold infections necessitated to review aspergillosis rodent models. The scope of this review has two major aspects. (1) It briefly summarizes Aspergillus toxicoses, the adverse effects of Aspergillus mycotoxins, the virulence factors of Aspergillus fumigatus, and how mild Aspergillus infections can turn to immunosuppressive diseases, ultimately to lethal invasive pulmonary aspergillosis. (2) The second major aspect of the review deals with earlier and recent murine models of pulmonary aspergillosis. Particular attention will be paid to the development of unified and generally applicable methods to detect, follow, and combat aspergillosis by medical treatments. Additionally, the review raises the question of responsibility regarding the application of immunosuppressive agents that initiate, contribute, and aggravate aspergillosis. Future studies of immunosuppression by chemical agents impacting aspergillosis deserve more studies.

Rough brucella strain RM57 is attenuated and confers protection against Brucella melitensis.

Brucella melitensis (B. melitensis) is a facultative intracellular pathogen, which is the main epidemic strain in China. To overcome disadvantages of traditional live attenuated vaccines, in this study a rough mutant RM57 was induced from a B. melitensis isolate M1981. In order to uncover the reason of changes in the LPS of RM57, the nucleotide sequences and transcription levels of all known genes related to LPS synthesis were detected. As LPS plays an important role in outer membrane integrity, the sensitivities of RM57 to SDS and polymyxin B were examined. The results showed that the expression level of LPS genes of RM57 was not significantly changed, and RM57 was sensitive to polymyxin B, compared to its parent strain. In further study, the virulence and protective efficacy of RM57 in mice and guinea pigs were determined, and our data indicated that RM57 was attenuated and had good protection effects, especially in guinea pigs model. Overall, these results demonstrated that the artificially induced rough mutant strain RM57 was an efficacious vaccine candidate against the challenge of virulent B. melitensis. Our data presented here provided additional insight into the mechanism of LPS synthesis of Brucella spp.

Experimental viral evolution to specific host MHC genotypes reveals fitness and virulence trade-offs in alternative MHC types.

The unprecedented genetic diversity found at vertebrate MHC (major histocompatibility complex) loci influences susceptibility to most infectious and autoimmune diseases. The evolutionary explanation for how these polymorphisms are maintained has been controversial. One leading explanation, antagonistic coevolution (also known as the Red Queen), postulates a never-ending molecular arms race where pathogens evolve to evade immune recognition by common MHC alleles, which in turn provides a selective advantage to hosts carrying rare MHC alleles. This cyclical process leads to negative frequency-dependent selection and promotes MHC diversity if two conditions are met: (i) pathogen adaptation must produce trade-offs that result in pathogen fitness being higher in familiar (i.e., host MHC genotype adapted to) vs. unfamiliar host MHC genotypes; and (ii) this adaptation must produce correlated patterns of virulence (i.e., disease severity). Here we test these fundamental assumptions using an experimental evolutionary approach (serial passage). We demonstrate rapid adaptation and virulence evolution of a mouse-specific retrovirus to its mammalian host across multiple MHC genotypes. Critically, this adaptive response results in trade-offs (i.e., antagonistic pleiotropy) between host MHC genotypes; both viral fitness and virulence is substantially higher in familiar versus unfamiliar MHC genotypes. These data are unique in experimentally confirming the requisite conditions of the antagonistic coevolution model of MHC evolution and providing quantification of fitness effects for pathogen and host. These data help explain the unprecedented diversity of MHC genes, including how disease-causing alleles are maintained.

Epicutaneous immunotherapy results in rapid allergen uptake by dendritic cells through intact skin and downregulates the allergen-specific response in sensitized mice.

Epicutaneous immunotherapy onto intact skin has proved to be an efficient and safe alternative treatment of allergy in an animal model with various allergens and in children for cow's milk allergy. The aim of this study was to analyze the different steps of the immunological handling of the allergen when deposited on intact skin using an epicutaneous delivery system and its immune consequences in sensitized BALB/c mice. As expected, when applied on intact skin, OVA exhibits neither a passive passage through the skin nor any detectable systemic delivery. The current study demonstrates that, after a prolonged application on intact skin, OVA is taken up by dendritic cells in the superficial layers of the stratum corneum and transported, after internalization, to the draining lymph nodes, with variations according to the previous level of sensitization of the mice. When OVA is applied with the epicutaneous delivery system repeatedly, specific local and systemic responses are down-modulated in association with the induction of regulatory T cells. Besides providing new insights into skin function in the presence of allergens, this study indicates that the skin might have a tolerogenic role, at least when kept intact.

Bovine-associated CNS species resist phagocytosis differently.

BACKGROUND: Coagulase-negative staphylococci (CNS) cause usually subclinical or mild clinical bovine mastitis, which often remains persistent. Symptoms are usually mild, mostly only comprising slight changes in the appearance of milk and possibly slight swelling. However, clinical mastitis with severe signs has also been reported. The reasons for the differences in clinical expression are largely unknown. Macrophages play an important role in the innate immunity of the udder. This study examined phagocytosis and killing by mouse macrophage cells of three CNS species: Staphylococcus chromogenes (15 isolates), Staphylococcus agnetis (6 isolates) and Staphylococcus simulans (15 isolates). Staphylococcus aureus (7 isolates) was also included as a control. RESULTS: All the studied CNS species were phagocytosed by macrophages, but S. simulans resisted phagocytosis more effectively than the other CNS species. Only S. chromogenes was substantially killed by macrophages. Significant variations between isolates were seen in both phagocytosis and killing by macrophages and were more common in the killing assays. Significant differences between single CNS species and S. aureus were observed in both assays. CONCLUSION: This study demonstrated that differences in the phagocytosis and killing of mastitis-causing staphylococci by macrophages exist at both the species and isolate level.

Indirect competitive ELISA based on monoclonal antibody for the detection of 5-hydroxymethyl-2-furfural in milk, compared with HPLC.

In this study, a method for rapid detection of 5-hydroxymethyl-2-furfural (HMF) was investigated. Monoclonal antibody (anti-HMF) was prepared and evaluated by an indirect competitive ELISA (ic-ELISA) format. The optimized standard curve was y=-0.2097x+1.0432 [where x is the logarithm (base 10) of the values of the HMF concentration and y is the absorbance of ic-ELISA results tested at 490 nm] and the linear detection range was 0.008 to 32.768 mg/L. The percentage of cross-reactivity of HMF with 5 major furfural derivatives was less than 2.92%. Finally, the established ic-ELISA format was used to test HMF in milk, and compared with the result obtained by HPLC, which produced an error of about 0.3%. Based on the data in this experiment, we concluded that the established ic-ELISA format was reliable with a high specificity.

Impact of mouse pregnancy on thymic T lymphocyte subsets.

It has been reported that fetal lymphoid progenitor cells are acquired during gestation and are able to develop in the maternal mouse thymus into functional T cells. Moreover, previous pregnancies increase the number of fetal cells in the mother. In the present study, we investigated whether mouse pregnancy induces changes in T lymphocyte subsets in the maternal thymus. We determined the T lymphocyte subsets in two allogeneic cross-breedings, namely CBA/J×BALB/c (normal) and CBA/J×DBA/2 (abortion prone), and investigated the effects of the age and parity of the female, as well as pregnancy outcome, on thymocyte populations. In addition, hormonal effects were evaluated in a syngeneic combination (CBA/J×CBA/J). We found that during pregnancy both hormonal and allogeneic stimuli induced a reduction in the CD4(+)CD8(+) subset with an increase in the CD4(+)CD8(-) population. Only young females of the normal combination exhibited an increase in the CD4(-)CD8(+) population. All young mice showed an increase in CD4(+)CD25(+)FoxP3(+) T cells. Interestingly, the γδT thymus pool was increased in all females of the normal allogeneic pregnancy only, suggesting the participation of this pool in the observed beneficial effect of multiparity in this cross-breeding. Our results demonstrate that allogeneic pregnancies induce important variations in maternal thymocyte subpopulations depending on the age of the female and the male component of the cross-breeding.

[Morphofunctional changes of BALB/c and C57BL/6 mice's immune system under chronic bacterial gram-negative endotoxicosis].

Chronic endotoxicosis was modeled by subcutaneous injection of the sepharose in complex with LPS. In these conditions we have studied morphofunctional changes of the immune system of BALB/c and C57Bl/6 mice, which are characterized by the different types of the immune response (Th2 type is predominant in BALB/c, Th1--in C57Bl/6). In the 1st-7th day t in the serum of BALB/c mice the endotoxin level increased in 21.3 times, in C57Bl/6--in 20.6 times. The endotoxin antibodies significantly decreased in 1th-7th days, on the 14th day it increased in the serum of both mice's strains. Morphofunctional changes of the immune system after chronic endotoxicosis were different in BALB/c and C57BI/6 mice. On the 1th day after injection of LPS and sepharose, in the thymus of C57Bl/6 mice the cortex layer was exhausted because of cell death, in the thymus of BALB/c mice II-III stages of accidental involution were developed. On the 7-14th day after injection of LPS and sepharose in the spleen of C57Bl/6 mice T- and B-zones were hyperplastic, however in spleen of BALB/c mice only T-zone were enlarged. After LPS and sepharose injection changes of cytokine production synthesized by KonA activated splenic cells were found out. In both strains the level of proinflammatory cytokines--TNFalpha and IL-1beta decreased, as well the Th1-cytokine IL-2. The production o fTh2-cytokine - IL-4, significantly decreased only in C57BI/6 mice. We suggest that damaging effect of LPS injection is determined by predominant Th2 or Th2 types of the immune response.

Morphofunctional characteristic of the immune system in BALB/c and C57BL/6 mice.

Inbred animals serve as an adequate model to study the role of genetic factors in adaptive, disadaptive, and pathological processes. Morphofunctional study of the immune system was performed on intact BALB/c and C57Bl/6 mice. The structural and functional parameters of the immune system in BALB/c and C57Bl/6 mice differ under physiological conditions. In BALB/c mice, volume density of T zone in the spleen and production of IL-2, IL-3, IL-4, IL-10, and TNF-α were much higher than in C57Bl/6 mice. However, IL-12 production in BALB/c mice was lower than in C57Bl/6 mice. C57Bl/6 mice were characterized by higher cytostatic activity of splenic NK cells. The observed interstrain differences are genetically determined and contribute to the type of adaptive processes and different sensitivity of these mice to pathogenic agents.

Development and characterization of TrMab­6, a novel anti­TROP2 monoclonal antibody for antigen detection in breast cancer.

Trophoblast cell­surface antigen 2 (TROP2) is a type I transmembrane glycoprotein that is overexpressed in a number of cancer types, including triple­negative breast cancer. The current study aimed to develop a highly sensitive and specific monoclonal antibody (mAb) targeting TROP2, which could be used to evaluate TROP2 expression using flow cytometry, western blot analysis and immunohistochemistry by employing the Cell­Based Immunization and Screening (CBIS) method. The established anti­TROP2 mAb, TrMab­6 (mouse IgG2b, κ), detected TROP2 on PA­tagged TROP2­overexpressing Chinese hamster ovary­K1 (CHO/TROP2­PA) and breast cancer cell lines, including MCF7 and BT­474 using flow cytometry. Western blot analysis indicated a 40 kDa band in lysates prepared from CHO/TROP2­PA, MCF7 and BT­474 cells. Furthermore, TROP2 in 57/61 (93.4%) of the breast cancer specimens was strongly detected using immunohistochemical analysis with TrMab­6. In conclusion, the current study demonstrated that TrMab­6 may be a valuable tool for the detection of TROP2 in a wide variety of breast cancer types.

Interleukin-17-mediated control of parasitemia in experimental Trypanosoma congolense infection in mice.

BALB/c mice are highly susceptible to experimental Trypanosoma congolense infections, whereas C57BL/6 mice are relatively resistant. Infected highly susceptible BALB/c mice die of systemic inflammatory response syndrome. Because interleukin-17 (IL-17) and Th17 cells regulate inflammatory responses, we investigated their role in the pathogenesis of experimental African trypanosomiasis in mice. We show that the production of IL-17 by spleen and liver cells and the serum IL-17 level increased after T. congolense infection in mice. Interestingly, infected highly susceptible BALB/c mice produced more IL-17 and had more Th17 cells than infected relatively resistant C57BL/6 mice. Paradoxically, neutralization of IL-17 with anti-IL-17 monoclonal antibody in vivo induced higher parasitemia in both the susceptible and the relatively resistant mice. Interestingly, anti-IL-17 antibody-treated mice had higher serum levels of alanine aminotransferase and aspartate aminotransferase, and the production of IL-10 and nitric oxide by liver cells was markedly decreased. Moreover, recombinant IL-17-treated mice exhibited significantly faster parasite control and lower peak parasitemia compared to control mice. Collectively, these results suggest that the IL-17/Th17 axis plays a protective role in murine experimental African trypanosomiasis.

T lymphocytes specific for immunoglobulin allotype. I. Igh-1b-specific T cells demonstrated by suppression in vivo and cytotoxicity in vitro.

We show that determinants of IgG(2a) of C57BL/6 mice (Igh-1(b)) stimulate allotypespecific T cells in BALB/c mice. Such cells are detected in two different functional assays; chronic allotype suppression and T cell-mediated cytotoxicity. A population of suppressor T cells capable of inducing chronic Igh-1(b) suppression was demonstrated by rosetting procedures to possess Igh-1(b)-specific receptors, a result interpreted as indicating that suppressor T cells may act directly upon allotype-bearing B cells. From similar populations we were also able to demonstrate Igh-1(b)-specific cytotoxic T cells. Such cells were lytic for target myeloma cells expressing the Igh-1(b) allotype of IgG28, and were ineffective against a variant cell line failing to express Igh-1(b), and other target cell lines expressing different allotypes or isotypes. The similar specificity of suppressor T cells and cytotoxic T lymphocytes for Igh-1(b) allotype raises the possibility that the target in allotype suppression is a B cell, and that allotype-specific cytotoxic T cells may play some role in regulation of allotype expression in the suppressed state.