Stimulation of resistance to Taenia taeniaeformis in the rat by infection with Fasciola hepatica

Homologous resistance to F. hepatica and T. taeniaeformis and cross resistance between these two parasites was investigated in the rat. Rats given a primary infection with F. hepatica were challenged with either F. hepatica or T. taeniaeformis. Conversely rats given a primary infection with T. taeniaeformis were challenged with either F. hepatica or T. taeniaeformis.Infection with F. hepatica generated significant resistance against challenge with F. hepatica given 9 weeks later. Similarly, infection with T. taeniaeformis protected against challenge with T. taeniaeformis given 6 weeks later. Infection with F. hepatica also generated significant resistance against challenge with T. taeniaeformis given 4, 8 or 9 weeks later. Primary infection with T. taeniaeformis did not protect against challenge with F. hepatica.     

Interactions between eosinophils and antibodies: In vivo protective role against rat schistosomiasis

An original protocol of cell transfer from Schistosoma mansoni-infected rats to normal recipient rats is used to investigate the protective role of phagocytic cell populations, described as effector cells in vitro, against a challenge infection with S. mansoni. Nonadherent, eosinophil-enriched and -adherent, macrophage-rich cell preparations, injected via intradermal and subcutaneous routes at the precise site of exposure to cercariae, were able to significantly protect the recipient rats. The time-course study of this protective effect according to the time after infection of donor rats revealed that eosinophils were the major cell population involved in the early phase of infection (4 to 5 weeks), whereas macrophages could also be incriminated thereafter. A rosette assay using anti-immunoglobulin-coated erythrocytes indicated a sequence of the various antibody isotypes under study (IgG₁, IgG_2a, IgE) on the eosinophil surface, during the course of infection. As previously shown in vitro, cytophilic antibodies seemed to participate in the protective effect of eosinophils, since eosinophil-enriched cells from normal rats, sensitized in vitro with immune complexes present in infected rat serum, could also confer significant protection. These observations establish therefore the relevance between our previous in vitro studies and rat resistance to a challenge infection with S. mansoni, underlining the major role played by the interaction between antibodies and phagocytic cells (eosinophils and macrophages).     

The fate of Taenia taeniaeformis oncospheres in normal and passively protected rats

Rats were passively protected against challenge infection with Taenia taeniaeformis by the administration of immune serum. Macroscopic liver lesions were rarely seen following challenge. The fate of oncospheres was determined by histological examination of rat livers at various intervals after infection, and also by in vitro experimentation.Oncospheres were killed soon after exposure to immune serum in vitro, but numbers reaching the liver were not significantly different in both passively protected and control rats. Oncospheral reorganisation did not take place in passively protected rats. In control rats, only 20 per cent of oncospheres reaching the liver were able to undergo reorganisation. Developing larvae also appeared to be susceptible to host rejection mechanisms, especially between days 5 and 9 after infection.     

Trypanosoma lewisi: antibody classes which mediate precipitation, agglutination, and the inhibition of reproduction

Sera from Trypanosoma lewisi-infected and uninfected rats were applied to Protein A-Sepharose CL-4B columns. The absorbed fractions of antisera which contained only IgG molecules were reacted in microimmunodiffusion analyses with the exoantigens of T. lewisi in plasma collected from irradiated infected rats, and formed one precipitin line. These sera were also applied to T. lewisi extract immunoabsorbent columns and bound proteins were eluted and analyzed by immunodiffusion against antisera specific for rat immunoglobulins. IgG₁, IgG_2a, IgG_2b, IgG_2c, and IgM were absorbed by the immuno-absorbent columns. Absorption of the rat antisera with anti-rat IgG or anti-rat IgM removed one of the two precipitin lines against extracts prepared from parasites collected from irradiated infected animals. The absorbed IgG fractions and nonabsorbed fractions of antisera which were collected after Protein A-Sepharose CL-4B column chromatography agglutinated trypanosomes. After treatment of antisera with 2-mercaptoethanol, the agglutinin titers were lower than those of the control antisera suggesting both IgG and IgM are involved in the agglutination. The ablastic activity of the fractions eluted from Protein A-Sepharose CL-4B Chromatographic columns was assayed in cultures of bloodstream forms ofT. lewisi. Ablastic activity of proteins of antisera absorbed by the columns was demonstrated indicating they belonged to the IgG class of antibodies.     

Acetylcholinesterase secretion by parasitic nematodes. IV. Antibodies against the enzyme in Trichostrongylus colubriformis infected sheep

Sheep infected with the nematode parasite Trichostrongylus colubriformis showed anti-T. colubriformis acetylcholinesterase. (AChE) antibodies in the IgG₁ but not the IgG₂ or IgM fractions prepared from their serum. Using the fluorescent antibody technique with representative sera, antibodies in the IgG₁ fraction exhibited specificity for antigens in the subventral glands of the worm excretory system. IgA antibody specificity for antigens in the excretory glands and intestine of the worm was also demonstrated.     

In vitro inhibition of the helper activity of GAT-specific T-cell lines by a syngeneic anti-idiotypic serum: preferential effect on the IgG response

We described in this paper the characteristics of a syngeneic anti-idiotypic serum made in BALB/c against BALB/c anti-poly (Glu⁶⁰ Ala³⁰ Tyr¹⁰) (GAT) antibodies. This serum recognizes idiotypic determinants present in all anti-GAT sera whatever the allotypic markers of the mice used to prepare the sera. The functional effect of this serum on two helper cell lines is also described. Cell line BDF₁/52 was obtained from GAT immunized lymph node cells (LNC). Cell line BDF₁/E₃ was selected from splenic T-cells educated in vitro on GAT-pulsed adherent cells. Both lines were propagated in presence of filler cells, antigen, and medium containing T-cell growth factor(s) from splenic cells activated with concanavalin A. Both cell lines exhibit a helper activity as measured by the plaque-forming cell (PFC) response they induce in vitro in the presence of DNP-GAT and DNP sensitized B cells. Their helper activity is specific and they require a hapten-carrier bridge to activate B cells. These lines are able to induce IgG₁, IgG_2a and IgG_2b anti-TNP PFC. Syngeneic anti-idiotypic serum B 658 inhibits specifically the function of these two lines but does not affect the helper activity of an OVA-specific T-cell line. The blocking activity of the serum can be adsorbed on a hybridoma protein with anti-GAT activity. This inhibition affects more dramatically the IgG₁ response than the IgG_2a and IgG_2b responses.     

Hepatic mast cells in rats infected with Taenia taeniaeformis

Mast cells appeared in the liver around metacestodes of Taenia taeniaeformis by 13 days after infection (DAI) of rats. The cells often occurred in clusters. The population increased until 28 DAI, then gradually declined. These hepatic mast cells (HMC) were compared to intestinal mucosal mast cells (MMC) and connective tissue mast cells (CTMC) histochemically, morphologically and in their response in vivo to Compound (built|48/80) and dexamethasone. Hepatic mast cells were similar to MMC in that they stained strongly blue with Astra blue at pH 1·0, could not be demonstrated with 0·005% toluidine blue, disappeared after treatment with dexamethasone, and were unaffected by 48/80. Immunoglobulin-containing cells in the liver were characterized by immunofluorescence. Immunoglobulin E-positive, and to a lesser extent IgG_2a-, and IgG_2c-positive cells surround the parasites in increasing numbers until 28 DAI, then declined. Many IgE-positive cells were HMC, and the IgE was frequently located intracytoplasmically. These cells were clearly distinguishable from eosinophils which stained characteristically with Giemsa and did not react with the anti-IgE probe. The results suggest that mast cell progenitors may be induced to localize and proliferate at the host-parasite interface in the Taenia-infected livers, giving rise to a cell population comparable to the MMC often seen at parasitized mucosal surfaces.     

Dietary omega-3 fatty acids enhance the B1 but not the B2 cell immune response in mice with antigen-induced peritonitis

The effects of omega-3 fatty acids on the adaptive immune response have mainly been analysed in vitro with varying results. How omega-3 fatty acids affect the adaptive immune response in vivo is largely unknown. This study examined the effects of dietary fish oil on the adaptive immune response in antigen-induced inflammation in mice, focusing on its effects on B cells and B cell subsets. Mice were fed a control diet with or without 2.8% fish oil, immunized twice with methylated BSA (mBSA) and peritonitis induced by intraperitoneal injection of mBSA. Serum, spleen and peritoneal exudate were collected prior to and at different time points after induction of peritonitis. Serum levels of mBSA-specific antibodies were determined by ELISA and the number of peritoneal and splenic lymphocytes by flow cytometry. The levels of germinal center B cells and IgM⁺, IgG⁺ and CD138⁺ cells in spleen were evaluated by immunoenzyme staining. Mice fed the fish oil diet had more peritoneal B1 cells, more IgM⁺ cells in spleen and higher levels of serum mBSA-specific IgM antibodies compared with that in mice fed the control diet. However, dietary fish oil did not affect the number of peritoneal B2 cells, splenic IgG⁺ or CD138⁺ cells or serum levels of mBSA-specific IgG antibodies in mice with mBSA-induced peritonitis. These results indicate that dietary fish oil can enhance the adaptive immune response, specifically the B1 cell response, which may lead to better protection against secondary infection as well as improvement in reaching homeostasis following antigenic challenge.     

Fasciola hepatica: Comparative studies on fascioliasis in rats and mice

Chapman C. B. and Mitchell G. F. 1982. Fasciola hepatica: comparative studies on fascioliasis in rats and mice. International Journal for Parasitology12: 81–91. Certain characteristics of infection differ between rats and mice exposed to metacercariae of the trematode parasite, Fasciola hepatica. Rats develop a degree of age-related resistance (and infected older females contain fewer parasites than older males), resistance to reinfection in infected rats is demonstrated readily though is partial, and a comparable degree of resistance can be obtained in recipients of infected rat serum provided the serum is given at about the time of challenge. None of these features of F. hepatica infection is seen in mice. Rats also differ from mice in that they can be vaccinated against infection (although again, resistance is incomplete) using larval antigen mixtures in adjuvants. Mice do respond to infection by production of antilarval antibodies and a slight IgG₁ hypergammaglobulinaemia and larvae will sensitize mice for delayed hypersensitivity. The results of this study indicate that sera from infected rats versus infected mice will be useful in pinpointing antigens of F. hepatica larvae which are involved in expression of partial host protection.     

Colonic Immune Stimulation by Targeted Oral Vaccine

Background

Currently, sufficient data exist to support the use of lactobacilli as candidates for the development of new oral targeted vaccines. To this end, we have previously shown that Lactobacillus gasseri expressing the protective antigen (PA) component of anthrax toxin genetically fused to a dendritic cell (DC)-binding peptide (DCpep) induced efficacious humoral and T cell-mediated immune responses against Bacillus anthracis Sterne challenge.

Methodology/Principal Finding

In the present study, we investigated the effects of a dose dependent treatment of mice with L. gasseri expressing the PA-DCpep fusion protein on intestinal and systemic immune responses and confirmed its safety. Treatment of mice with different doses of L. gasseri expressing PA-DCpep stimulated colonic immune responses, resulting in the activation of innate immune cells, including dendritic cells, which induced robust Th1, Th17, CD4⁺Foxp3⁺ and CD8⁺Foxp3⁺ T cell immune responses. Notably, high doses of L. gasseri expressing PA-DCpep (10¹² CFU) were not toxic to the mice. Treatment of mice with L. gasseri expressing PA-DCpep triggered phenotypic maturation and the release of proinflammatory cytokines by dendritic cells and macrophages. Moreover, treatment of mice with L. gasseri expressing PA-DCpep enhanced antibody immune responses, including IgA, IgG₁, IgG_2b, IgG_2c and IgG₃. L. gasseri expressing PA-DCpep also increased the gene expression of numerous pattern recognition receptors, including Toll-like receptors, C-type lectin receptors and NOD-like receptors.

Conclusion/Significance

These findings suggest that L. gasseri expressing PA-DCpep has substantial immunopotentiating properties, as it can induce humoral and T cell-mediated immune responses upon oral administration and may be used as a safe oral vaccine against anthrax challenge.     

Characterization of sheep antibodies involved in precipitate formation with surface antigens of Fasciola hepatica in vitro

Sandeman R. M. and Howell M. J. 1982. Characterization of sheep antibodies involved in precipitate formation with surface antigens of Fasciola hepatica in vitro. International Journal for Parasitology12: 467–471. The role of sheep antibodies which precipitate with surface antigens of Fasciola hepatica is unclear. In an attempt to clarify their function these antibodies were characterized as to their immunoglobulin class and ability to affect the survival of fluke in rats. The ability of fluke antigens complexed with sheep antibody to vaccinate rats against infection was also tested. IgM antibodies were involved in precipitate formation on the teguments of fluke 3 weeks after infection but IgG₁ predominated at later stages of infection. The decreased survival of fluke in rats after culture with increasing levels of sheep antibodies suggests that the antibodies exert some deleterious effect on the fluke in vitro. The fluke antigen-sheep antibody complex failed to immunize rats against infection. Since sheep antibodies to F. hepatica can impair the ability of fluke to resist further attack in rats but not sheep, it is suggested that some effector mechanism other than antibody is defective in the latter.     

Trypanosoma cruzi: the T-cell dependence of the primary immune response and the effects of depletion of T cells and Ig-bearing cells on immunological memory

The effects of T-cell depletion on primary infection with Trypanosoma cruzi and on immunological memory to this parasite were studied in a syngeneic mouse system. Exacerbation of T. cruzi infections occurred in thymectomized, irradiated, bone marrow-reconstituted (TX) C57BL/6J mice compared to sham thymectomized, irradiated, bone marrow-reconstituted (STX) mice. Reconstitution of TX mice with thymocytes restored the resistance to a level equivalent to that of STX mice. Immunological memory against T. cruzi present in spleen cells in mice recovered from T. cruzi infections could be ablated by treatment with rabbit anti-brain-associated theta serum but not with rabbit anti-mouse immunoglobulin serum prior to adoptive transfer of immune spleen cells into TX mice. These experiments suggest that modulation of the primary immune response and memory against T. cruzi depends largely on the thymus-derived lymphocyte. The possible implications of this T-cell regulation on previously reported effector mechanisms againt this parasite are discussed.     

Immunity against trichostrongylus colubriformis infection in guinea-pigs and sheep: Some comparisons with Nippostrongylus brasiliensis infection in the rat

In Nippostrongylus brasiliensis infection in rats there is evidence that antibodies ‘damage’ the worms rendering them susceptible to other components of the host immune response. Some of the experiments from which this evidence was obtained were repeated in Trichostrongylus colubri-formis infections in guinea-pigs and sheep.Lesions similar to those described in ‘damaged’ N. brasiliensis were present in T. colubriformis, but unlike damaged N. brasiliensis, damaged T. colubriformis were not rapidly expelled from the intestine of either normal or adoptively immunized hosts. Other differences between the two infections included the failure of serum from T. colubriformis-immune donors either to regularly transfer immunity against infection to non-immune recipients or to endow additional immunity on recipients of lymphoid cells from immune donors.It is suggested that the results might reflect differences between the manner in which guinea-pigs and rats achieve immune expulsion of gastro-intestinal nematode parasites.     

Further studies of the therapeutic effectsof murine melanoma-specific monoclonal antibodies

The results presented here further characterize four murine monoclonal antibodies (mAb) that recognize melanoma-specific antigens (9B6, T97, 2-3-1 and 2-3-3). These melanoma-specific mAbs are of the IgG_2b isotype and are significantly therapeutic when administered systemically against established pulmonary melanoma metastases. Here we show a consistent and significantly inhibition of the growth of melanoma lung metastases by all four mAbs and the existence of a time ‘window’ at days 5–8 after tumor inoculation for optimal therapy. Since these mAbs were found not to be cytotoxic or cytolytic in vitro, we looked for host immune response regulation as being responsible for the therapeutic effects. Natural killer (NK) cells were implication as one arm of the host immune system involved in this response since depletion of NK cells in vivo by αasialoGM1 or αNK1.1 antibodies partially abrogated the inhibitory effect of the mAbs. The observed antimetastatic effects could also be partially abrogated using antibodies directed against the T-cell subset surface markers, CD4⁺ and CD8⁺. Intramuscular melanoma tumor growth was also found to be suppressed by mAb 2-3-1, but only if administered in the area of tumor growth and only if multiple inoculations are administered over a 13-day period. The beneficial effect of mAb antimetastatic therapy was found to be useful against several syngeneic melanomas, including JB/MS, B16 and several sublines of the B16 F10 melanoma.     

2B4 Is Dispensable for T-Dependent B Cell Immune Responses,but Its Deficiency Leads to Enhanced T-Independent Responses Due to an Increase in Peritoneal Cavity B1b Cells

The signaling lymphocyte activation molecule (SLAM) family plays important roles in adaptive immune responses. Herein, we evaluated whether the SLAM family member 2B4 (CD244) plays a role in immune cell development, homeostasis and antibody responses. We found that the splenic cellularity in Cd244 ^-/- mice was significantly reduced due to a reduction in both CD4 T cells and follicular (Fo) B cells; whereas, the number of peritoneal cavity B cells was increased. These findings led us to examine whether 2B4 modulates B cell immune responses. When we examined T-dependent B cell responses, while there was no difference in the kinetics or magnitude of the antigen-specific IgM and IgG₁ antibody response there was a reduction in bone marrow (BM) memory, but not plasma cells in Cd244 ^-/- mice. When we evaluated T-independent immune responses, we found that antigen-specific IgM and IgG₃ were elevated in the serum following immunization. These data indicate that 2B4 dampens T-independent B cell responses due to a reduction in peritoneal cavity B cells, but has minimal impact on T-dependent B cell responses.     

Taenia crassiceps antigens induce a Th2 immune response and attenuate injuries experimentally induced by neurotoxoplasmosis in BALB/c mice

Toxoplasma gondii is a pathogenic agent responsible for causing both systemic and local disease which elicits a typically pro-inflammatory, Th1 immune response. Taenia crassiceps antigen induces a Th2 immune response that immunomodulates Th1 based infections. Therefore the aim of this study was to evaluate whether T. crassiceps cysticerci antigens are able to modulate the inflammatory response triggered in experimental neurotoxoplasmosis (NT). BALB/c mice were inoculated with T. gondii cysts and/or cysticerci antigens and euthanized at 60 and 90 days after inoculation (DAI). The histopathology of the brains and cytokines produced by spleen cells culture were performed. The animals from the NT group, 90DAI (NT90), presented greater intensity of lesions such as vasculitis, meningitis and microgliosis and cytokines from Th1 profile characterized by high levels of IFN-gamma. While in the T. crassiceps antigens group, 60DAI, there were more discrete lesions and high levels of IL-4, a Th2 cytokine. In the NT co-inoculated with cysticerci antigens group the parenchyma lesions were more discrete with lower levels of IFN-gamma and higher levels of IL-4 when compared to NT90. Therefore the inoculation of T. crassiceps antigens attenuated the brain lesions caused by T. gondii inducing a Th2 immune response.     

Effects of dietary cholesterol on antioxidant capacity,non-specific immune response,and resistance to Aeromonas hydrophila in rainbow trout (Oncorhynchus mykiss) fed soybean meal-based diets

This study evaluated the effects of dietary cholesterol on antioxidant capacity, non-specific immune response and resistance to Aeromonas hydrophila in rainbow trout (Oncorhynchus mykiss) fed soybean meal-based diets. Fish were fed diets supplemented with graded cholesterol levels (0 [control], 0.3, 0.6, 0.9, 1.2, and 1.5%) for nine weeks. The fish were then challenged by A. hydrophila and their survival rate recorded for the next week. Dietary cholesterol supplementation generally increased the serum and hepatic superoxide dismutase (SOD), glutathione-peroxidase (GSH-Px), catalase (CAT), and total antioxidant capacity (TAC) activities, but decreased the serum and hepatic malondialdehyde (MDA) contents. Further, the hepatic CAT and serum SOD, CAT, and TAC activities were significantly higher in fish fed diets supplemented with 0.9 or 1.2% cholesterol compared to those fed the control diet, whereas the serum and hepatic MDA contents were significantly lower. The respiratory burst activity, alternative complement activity, and hepatic lysozyme activity increased steadily when the supplemental cholesterol was increased by up to 1.2% and then declined with further addition. The serum lysozyme activity and phagocytic activity increased steadily with increasing dietary supplemental cholesterol level up to 0.9% and then declined with further addition. Dietary cholesterol supplementation generally enhanced the protection against A. hydrophila infection, and fish fed diets supplemented with 0.9 or 1.2% cholesterol exhibited the highest post-challenge survival rate. The results indicated that cholesterol may be under-supplied in rainbow trout fed soybean meal-based diets, and dietary cholesterol supplementation (0.9–1.2%) contributed to improved immune response and disease resistance of rainbow trout against A. hydrophila.     

Immunization against Taenia taeniaeformis in mice: studies on the characterization of antigens from oncospheres

Mature eggs of Taenia taeniaeformis hatched readily in the presence of sodium hypochlorite and no loss in infectivity of oncospheres for mice was observed after hatching. Crude and sodium deoxycholate-solubilized antigens (termed TtO-DOC) prepared from such oncospheres stimulated high levels of protection against T. taeniaeformis infection in immunized mice similar to those described previously for oncospheres prepared by other methods. Mice immunized with TtO-DOC antigens that had been exposed to potassium metaperiodate remained significantly protected against infection. Exposure of TtO-DOC antigens to pronase and thermolysin, or to trypsin, significantly reduced the ability of these antigens to protect mice against infection. These data suggest that the antigens which immunize mice against infection include protein components. ¹²⁵I-labelled TtO-DOC antigens were immunoprecipitated with sera from mice infected with T. taeniaeformis and the immunoprecipitates analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Immunoprecipitation with sera from C3H/He mice infected for 28 days revealed a single major labelled protein antigen having a relative molecular mass (M_r) of 31,000. Sera from 5-month infected C3H/He mice immunoprecipitated at least thirteen labelled antigens, including one at M_r 31,000. Attempts to use SDS-PAGE separated proteins to immunize mice showed that oncosphere antigens exposed to the reducing conditions prior to SDS-PAGE lost their ability to protect mice against infection. It was concluded that SDS-PAGE was an unsatisfactory technique for the isolation of a host protective fraction of TtO-DOC antigens. TtO-DOC proteins were resolved by PAGE performed in the presence of sodium deoxycholate (DOC-PAGE) and mice were vaccinated with cut-outs from the gel. A fraction of the DOC-polyacrylamide gel was found to be effective in immunizing mice against infection. Thus, although the characteristics of the protein antigens in this DOC-PAGE fraction have yet to be determined, an important fractionation technique has been identified. It was shown that partial removal of DOC from oncosphere antigen preparations solubilized in 1% DOC was required for the antigen to stimulate protective immunity. These findings will facilitate further antigen characterization studies towards the development of a defined-antigen vaccine in murine cysticercosis. This is particularly so as attempts to raise anti-oncospheral monoclonal antibodies capable of passively transferring protection to mice by using crude antigen preparations to immunize donor mice have not been successful.     

Large-Scale In Vitro Expansion of Polyclonal Human Switched-Memory B Lymphocytes

Polyclonal preparations of therapeutic immunoglobulins, namely intravenous immunoglobulins (IVIg), are essential in the treatment of immunodeficiency and are increasingly used for the treatment of autoimmune and inflammatory diseases. Currently, patients’ accessibility to IVIg depends exclusively upon volunteer blood donations followed by the fractionation of pooled human plasma obtained from thousands of individuals. Presently, there are no in vitro cell culture procedures allowing the preparation of polyclonal human antibodies. All in vitro human therapeutic antibodies that are currently generated are based on monoclonal antibodies, which are mostly issued from genetic engineering or single cell antibody technologies. Here, we describe an in vitro cell culture system, using CD40-CD154 interactions, that leads to a 1×10⁶-fold expansion of switched memory B lymphocytes in approximately 50 days. These expanded cells secrete polyclonal IgG, which distribution into IgG₁, IgG₂, IgG₃ and IgG₄ is similar to that of normal human serum. Such in vitro generated IgG showed relatively low self-reactivity since they interacted moderately with only 24 human antigens among a total of 9484 targets. Furthermore, up to one liter of IgG secreting cells can be produced in about 40 days. This experimental model, providing large-scale expansion of human B lymphocytes, represents a critical step toward the in vitro production of polyclonal human IgG and a new method for the ex vivo expansion of B cells for therapeutic purposes.     

Adjuvant and immunogenic properties of bacterial lipopolysaccharide in IgE and IgG1 antibody formation in mice

The ability of Gram-negative lipopolysaccharide (LPS) to function as an adjuvant and as an antigen in IgE and IgG₁ immune responses in mice was investigated. LPS failed to induce LPS-specific IgE or IgG₁ under a variety of experimental conditions. Both isolated LPS and whole heat-killed bacteria were capable of enhancing IgE and IgG₁ antibody formation to a protein antigen, egg albumin (EA). The LPS-induced anti-EA, IgE, and IgG₁ antibody titers exhibited a cycling phenomenon with time. In the presence of LPS, IgE, and IgG₁ antibodies specific for EA did not occur in athymic nude (BALB/c-nu/nu) mice, demonstrating the inability of LPS to substitute for the stringent requirement for T cells in homocytotropic antibody formation.