Pulmonary inflammation in parasitic infection: immunoglobulins in bronchoalveolar washings of rats infected with Nippostrongylus brasiliensis

Despite marked pulmonary pathology caused by larval stages of many helminth parasites, little is known about the mechanisms of immune and inflammatory responses to parasites in the respiratory tract. Using bronchoalveolar lavage (BAL) we have retrieved soluble proteins and cells from the respiratory tract of rats given a primary or secondary infection with the nematode Nippostrongylus brasiliensis. Total amounts of different immunoglobulin classes and albumin in BAL fluids and serum were quantitated using an ELISA. Analysis of the cellular component showed an increase in alveolar macrophages, neutrophils, eosinophils and lymphocytes on different days post-infection similar to our earlier findings. A time course study revealed that the concentrations of total protein, albumin, IgG, IgA and IgM in BAL fluids of infected animals were increased from days 2 to 32 after a primary infection. The magnitude of this increase was higher following a challenge infection (secondary) with the same parasite. Moreover, there was also a biphasic increase in total protein, IgG and IgA after secondary infections, with peaks on days 2 to 4 and 11 to 21 post-infection. A comparison of immunoglobulin to albumin ratios in serum and BAL fluids showed that the initial peak of proteins in the lavage was a result of serum leakage and the subsequent peak was due to local secretion of immunoglobulins. These results suggest that in addition to marked BAL cellular reactivity, N. brasiliensis infection induces an initial vascular and endothelial permeability in the respiratory tract which is soon repaired but followed by local synthesis and secretion of IgG and IgA in the lower respiratory tract.     

Kinetics of immunoglobulin and specific antibody responses of CBA mice infected with Trypanosoma rhodesiense

Summary Groups of CBA/CaJ and B-cell deficient CBA/N mice were infected with Trypanosoma rhodesiense EATRO 1886 strain. Survival, parasitaemia, serum Ig levels plus specific trypanosomal IgM and IgG antibodies were assayed and compared during infection. Whereas both strains of mice had similar parasitaemias during the first week of infection, CBA/N parasitaemias were lower than those observed in CBA/CaJ mice during the subsequent study period. Antibody responses, specific for T. rhodesiense antigens, peaked on day 10 after infection in CBA/CaJ mice, then rapidly declined. However, antibody responses in CBA/N mice remained elevated throughout the study. In addition, the kinetics of specific IgG and IgM varied in CBA/N mice: IgG antibody was detected on day 4, whereas specific IgM was detected on day 16. This unique relationship between the appearance of IgG and IgM antibody may explain the longer survival observed for B-cell deficient CBA/N mice infected with T. rhodesiense.     

Tropical pulmonary eosinophilia: analysis of antifilarial antibody localized to the lung

Acute tropical pulmonary eosinophilia (TPE) is characterized by wheezing, pulmonary infiltrates, marked peripheral blood eosinophilia, and very high serum levels of filaria-specific antibodies. To evaluate the amount and character of the filaria-specific antibodies in the lungs in this disorder, bronchoalveolar lavage was carried out in individuals with acute TPE, in normal subjects, and in patients with elephantiasis or asthma. Striking elevations of total IgE were found in the lower respiratory tract epithelial lining fluid (ELF) of patients with TPE along with high levels of filarial-specific IgG, IgM, and IgE. When patients with acute TPE were treated with diethylcarbamazine and evaluated again 6-14 d later, there was marked reduction in ELF parasite-specific IgG and IgE, which paralleled a rapid clinical response. Immunoblot comparison of the antigen recognition patterns of ELF and serum antibodies demonstrated a general similarity in parasite antigens recognized, but the lung IgE and IgG antibodies appeared to recognize only a certain subset of the parasite antigens recognized by serum antibodies. Thus, a profound antibody response to filarial infection is found in the lungs of patients with TPE, suggesting that these filaria-specific antibodies play an important role in the pathogenesis of this disorder.     

Immunological Responses to Seoul Orthohantavirus in Experimentally and Naturally Infected Brown Rats (Rattus norvegicus)

To clarify the mechanism of Seoul orthohantavirus (SEOV) persistence, we compared the humoral and cell-mediated immune responses to SEOV in experimentally and naturally infected brown rats. Rats that were experimentally infected by the intraperitoneal route showed transient immunoglobulin M (IgM) production, followed by an increased anti-SEOV immunoglobulin G (IgG) antibody response and maturation of IgG avidity. The level of SEOV-specific cytotoxic T lymphocytes (CTLs) peaked at 6 days after inoculation and the viral genome disappeared from serum. In contrast, naturally infected brown rats simultaneously had a high rate of SEOV-specific IgM and IgG antibodies (28/43). Most of the IgM-positive rats (24/27) had the SEOV genome in their lungs, suggesting that chronic SEOV infection was established in those rats. In female rats with IgG avidity maturation, the viral load in the lungs was decreased. On the other hand, there was no relationship between IgG avidity and viral load in the lungs in male rats. A CTL response was not detected in naturally infected rats. The difference between immune responses in the experimentally and naturally infected rats is associated with the establishment of chronic infection in natural hosts.     

The detection and measurement of coproantibodies to Nippostrongylus brasiliensis in rats following a primary infection

Summary Investigations were initiated to study the possible detection and measurement of coproantibodies in animals infected with a gastrointestinal nematode parasite. Faecal extracts, extracts of small intestinal mucosa and sera of rats infected with intestinal nematode Nippostrongylus brasiliensis were examined for total IgA, IgM and IgG levels and haemagglutinating and precipitating antibodies specific to parasite antigens over a 30-day-period following infection. It was found that in both faecal and mucosal extracts immunoglobulin concentrations increased after a primary infection. In faecal extracts there was a seven-fold increase of IgA, a three to six-fold increase of IgG and about a fifty-fold increase of IgM. Haemagglutinins in faecal extracts detected by adult worm excretory-secretory (ES) products and adult worm and infective larvae somatic extracts were observed from 3 days after infection (DAI). Haemagglutinins detected by ES products reached their highest titres on 11–12 DAI while those reacting with adult worm somatic extracts showed the highest level between IS and 19 DAI. A similar pattern of response was found in the antibody levels of the intestinal mucosa. Haemagglutinins detected in faeces during the first 12 DAI reacted with the same antigens as antibodies present in the sera at that time but coproantibodies from 18, 24 and 30 DAI were different from those circulating in sera at that stage of the infection. The results suggest that measurement of coproantibody levels may provide a convenient and useful index of local immune responses to gastrointestinal helminths.     

Local antibody production and immune complex formation in rats experimentally infected with Angiostrongylus cantonensis

The systemic humoral immune responses and tissue localization of worm-antigen, antibodies (IgG), and complement (C3) were examined in rats experimentally infected with Angiostrongylus cantonensis. While the worms remained in the subarachnoid space, it was infiltrated with plasma cells and lymphoid cells containing IgM and IgG. When the infiltration of these cells became more pronounced, the serum antibody titer began to increase. At the same time, deposits of IgM, IgG, and C3 were found in the glomeruli of the kidney. A number of eggs were observed in the lungs, enclosed in granulomatous tissues. Infiltrates of plasma cells including IgM and IgG, and deposits of IgM, IgG, and C3 were detected around the eggs and in the granulomatous tissues. A marked increase in serum antibody was observed. A. cantonensis larvae induce local antibody (IgM and IgG) production in the central nervous system prior to an increase of serum antibody titer. Measurement of cerebrospinal fluid antibody titer at an early stage of infection may confirm infection. The larvae showed no evidence of damage in spite of marked local antibody production in the central nervous system. The eggs in the lungs stimulated both local and systemic antibody production, and immune complexes were formed in the lung and the circulatory system. Immune complexes may participate in the formation of granuloma.     

Pulmonary and serum isotypic antibody responses of mice to live and inactivated influenza virus

Primary and secondary immunoglobulin class-specific antibody responses in serum and pulmonary lavage fluids of mice were studied after respiratory infection and intramuscular vaccination with influenza virus. Infection and vaccination with inactivated virus vaccine induced primary IgM and IgG antibody responses in the serum and pulmonary lavage fluids (PLF). Neither immunizing method induced detectable serum IgA antibodies, and only infection generated IgA antibodies in PLF. The major portion of antibodies in PLF was derived from serum, but local synthesis of IgG and IgA antibodies was detected after virus infection. Vaccination of infection-primed mice boosted the IgM and IgG antibody concentrations in serum and PLF but had no effect on IgA antibody concentrations. Nonlethal infection of vaccine-primed mice generated secondary IgM and IgG antibody responses in serum and PLF and an IgA antibody response in PLF. Again, most of the antibody detected in PLF was derived from serum, but low concentrations of IgA and IgG were synthesized locally after infection. Although mice immunized with inactivated vaccine lacked the capacity to synthesize IgA antibody, they were protected from severe pulmonary disease when challenged with lethal influenza virus. These data support the concept that serum IgG antibodies are sufficient for prevention of severe pulmonary disease.     

Stem cell factor contributes to intestinal mucosal mast cell hyperplasia in rats infected with Nippostrongylus brasiliensis or Trichinella spiralis, but anti-stem cell factor treatment decreases parasite egg production during N brasiliensis infection

We assessed the effects of the c-kit ligand, stem cell factor (SCF), in the jejunal mucosal mast cell hyperplasia that occurs during infection with the intestinal nematodes, Nippostrongylus brasiliensis or Trichinella spiralis in rats. Compared with vehicle-treated rats, rats treated with SCF (25 micrograms/kg/d, intravenous [i.v.] for 14 days) during N brasiliensis infection exhibited significantly higher levels of the rat mucosal mast cell (MMC)-associated protease, rat mast cell protease II (RMCP II) in the jejunum and serum on day 8 of infection, but not on days 10 or 15 of infection. By contrast, in comparison to rats treated with normal sheep IgG, rats treated with a polyclonal sheep antirat SCF antibody exhibited markedly decreased numbers of jejunal MMCs, levels of jejunal RMCP II, and serum concentrations of RMCP II during infection with either nematode, particularly at the earlier intervals of infection (< or = day 10). Taken together, these findings indicate that SCF importantly contributes to MMC hyperplasia and/or survival during N brasiliensis or T spiralis infection in rats, but that levels of endogenous SCF are adequate to sustain near maximal MMC hyperplasia during infection with these nematodes. Notably, treatment of rats with SCF somewhat increased, and treatment with anti- SCF significantly decreased, parasite egg production during N brasiliensis infection. This finding raises the interesting possibility that certain activities of intestinal MMCs may contribute to parasite fecundity during infection with this nematode.     

A novel approach based on antigen, antibody and immune complex detection in bronchoalveolar lavage fluid samples from rats experimentally infected with Strongyloides venezuelensis

This study was performed in order to develop a novel approach based on antigen, antibody and immune complex detection by enzyme-linked immunosorbent assay (ELISA) in bronchoalveolar lavage fluid (BALF) samples. For that purpose Wistar rats immunosuppressed or not were experimentally infected with Strongyloides venezuelensis. The microtiter plates were coated with alkaline parasite extract for antibody detection and with IgG anti-S. venezuelensis for antigen and immune complex detection. The immune serum was able to detect 1.56μg/mL of L3 antigens in BALF samples. ELISA sensitivity was 96.6%, 71.6% and 91.6% for antigen, antibody and immune complex, respectively, and the specificity was 100% for all methods. Antigen detection in BALF samples showed to be a good approach for evaluating the kinetics of infection in non immunosuppressed or immunosuppressed rats. IgG was detected in non immunosuppressed rats from day 8 p.i. and in immunosuppressed rats from day 2 p.i. Moreover, immune complex was detected during the entire kinetic for both groups. In conclusion, association of antigen, antibody and immune complex detection in BALF samples seems to be an alternative approach for early strongyloidiasis diagnosis particularly in immunosuppressed individuals.     

Pulmonary inflammation and immune responses during the course of Nippostrongylus brasiliensis infection: lymphocyte subsets in bronchoalveolar lavage fluids of rats

Quantitative measurements were made of different phenotypes of lymphocytes in bronchoalveolar lavage fluid (BALF) of rats during the course of a primary or secondary infection with Nippostrongylus brasiliensis. These changes were compared with those in the peripheral blood to understand the site-specificity of the responses. Following infection, there was a significant increase in both B and T lymphocytes in BALF. The CD4: CD8 ratio was significantly altered with a decreased ratio on day 2 and increased ratio on days 16 and 32 post infection (p.i.). Two colour analysis showed that during larval migration through the lungs (day 2 p.i.) there was a significant increase in CD8+, CD4+ OX22+ and CD4+ OX22- cells in BALF. As infection progressed in time, CD4+ OX22 – cells were increased significantly. Compared to primary infection, a secondary infection resulted in increased recovery of CD4+ OX22– cells in BALF. These changes were not readily appreciated in the peripheral blood, suggesting site-specific compartmentalization of lymphocyte responses in the lung. The functional significance of these dynamic changes in lymphocyte subsets in the airspaces following infection remains to be identified.     

Acquisition of antibody isotypes against Plasmodium falciparum blood stage antigens in a birth cohort

Information on the period during which infants lose their maternally derived antibodies to malaria and begin to acquire naturally their own immune responses against parasite antigens is crucial for understanding when malaria vaccines may be best administered. This study investigated the rates of decline and acquisition of serum antibody isotypes IgG1, IgG2, IgG3, IgG4, IgM and IgA to Plasmodium falciparum antigens apical membrane antigen (AMA1), merozoite surface proteins (MSP1‐19, MSP2 and MSP3) in a birth cohort of 53 children living in an urban area in the Gambia, followed over the first 3 years of life (sampled at birth, 4, 9, 18 and 36 months). Antigen‐specific maternally transferred antibody isotypes of all IgG subclasses were detected at birth and were almost totally depleted by 4 months of age. Acquisition of specific antibody isotypes to the antigens began with IgM, followed by IgG1 and IgA. Against the MSP2 antigen, IgG1 but not IgG3 responses were observed in the children, in contrast with the maternally derived antibodies to this antigen that were mostly IgG3. This confirms that IgG subclass responses to MSP2 are strongly dependent on age or previous malaria experience, polarized towards IgG1 early in life and to IgG3 in older exposed individuals.     

Coccidiosis: characterization of antibody responses to infection with Eimeria nieschulzi

Summary The antibody responses of rats to infection with the intestinal intracellular protozoan parasite Eimeria nieschulzi were examined by a sensitive radio-immunoassay with a soluble preparation of sporulated oocysts as antigen. Specific antibodies of the IgM, IgGl, IgG2a and IgG2b isotypes were found in the blood circulation and IgA antibodies were detected in the bile and in intestinal washings. The IgM response was rapid, its peak was relatively brief and it was not recalled by the reinoculation of oocysts. There were some differences between the responses in the different subclasses of IgG but they all reached a peak between 20–30 days after the initiation of the primary infection and there was an anamnestic response to a challenge inoculation of oocysts. IgA antibodies to E. nieschulzi antigen in the bile and in intestinal washings increased and decreased after both primary and secondary inocula. Antibodies of all isotypes tested were virtually absent in the blood circulation of infected athymic rats. These findings are discussed with reference to antibody responses to other parasitic infections and to the role of antibodies in immunity to coccidiosis.     

The effect of Trypanosoma brucei infection on local and systemic antibody responses of rats to Nippostrongylus brasiliensis

Adult Hooded Lister rats were given 5000 Nippostrongylus brasiliensis larvae on day 3 or 7 after infection with Trypanosoma brucei and a second dose of 5000 nematode larvae 28 days later. A similar number of rats was infected only with N. brasiliensis larvae. Comparison of antibody levels in serum and the respiratory and alimentary tracts showed that T. brucei infection influenced both systemic and local antibody responses of rats to N. brasiliensis antigens. After primary infection systemic antibody responses were mainly impaired, the level of suppression depending upon the interval between trypanosome and nematode infections. Anamnestic responses were diminished in both antibody systems. The number of worms reaching the small intestine of T. brucei parasitised rats after primary infection was twice- and after reinfection three-times higher than in rats subjected to nematode infections alone. However, adult nematode expulsion was not delayed. The results suggest that N. brasiliensis infection causes a multiantigenic stimulation of both systemic and local humoral responses of the host. Furthermore, they indicate that depression of systemic antibody responses may enhance worm establishment.     

Antibody isotypes of immune complexes in schistosomiasis mansoni in Sudan

From a panel of monoclonal antibodies to Schistosoma mansoni, one that is specific to a shared cercarial and schistosomular antigen, and does not react with other major parasite species including Fasciola hepatica, was selected for use as an antigen-capture layer in a sandwich ELISA for detection of specific circulating immune complexes in the blood of S. mansoni-infected subjects from Sudan. The test, which identifies immune complexes of only a single antibody-bound antigen, is developed using human Ig class- and IgG subclass-specific enzyme (HRP)-antibody conjugates. European blood donor sera and those with rheumatoid factor and/or anti-nuclear antibody are negative in this test. The prevalence and distribution of the different antibody isotypes in antigen-specific complexes was determined in 276 subjects of four infection groups; primary school children, adult irrigation canal cleaners with chronic infections, an equivalent group of Praziquantel cured canal cleaners, and hospital-referred cases with severe hepatosplenic symptoms. The isotype profiles of antibodies in the specific complexes were compared with those in the total serum complexes prepared by polyethylene glycol precipitation. In chronic infections and in children there is a high prevalence of IgG and IgM specific complexes, the IgG being predominantly IgG1, with little or no IgG3 and IgG4. Treated chronic infections show reduced specific complexes in all classes of antibody. Compared with chronic and children's infections, a large proportion of the patients with severe infections have in addition to high IgM, high levels of IgG2, IgG3 and IgG4 specific complexes, a fact which suggests a causal relationship between antibody production in one or more of these subclasses to the circulating antigen and symptoms of hepatosplenic disease. Although all subjects have significant amounts of total serum complexes with IgG, untreated chronic infections have much higher concentrations than other infected groups. This group also has the highest levels and prevalence of IgM and IgE complexes. In treated chronic cases IgG and IgM total complexes are greatly reduced. The significant finding in patients with severe symptoms is the relatively high IgA immune complex level compared with other groups. Taken overall the results suggest that screening of populations in endemic regions for serum immune complexes by specific and non-specific means could offer valuable data on the significance of antibody responses to circulating antigens in different isotypes in relation to pathogenesis.(ABSTRACT TRUNCATED AT 400 WORDS)     

Prospective observational study of antiphospholipid antibodies in acute lung injury and acute respiratory distress syndrome: comparison with catastrophic antiphospholipid syndrome

Detection of antiphospholipid (aPL) antibodies in bronchoalveolar lavage fluid (BALF) of patient with acute respiratory distress syndrome (ARDS) suggests involvement of autoimmune mechanisms in the pathogenesis of ARDS. We investigated whether aPL antibodies could be detected in the serum as well as BALF of patients with acute lung injury (ALI) and ARDS. IgG anticardiolipin, IgG anti-beta2-glycoprotein I, IgG antiphosphatidic acid and IgG antiphosphatidylserine antibodies were detected by ELISA in low titers within the normal range in the BALF and serum of nine patients with ALI and 17 patients with ARDS. However, one out of 27 patients investigated had high levels of aPL antibodies in both BALF and serum. This patient suffered from severe ARDS due to sepsis. The high aPL antibody levels in serum possibly triggered by sepsis were associated with high aPL antibody levels in BALF, which can be explained by high capillary-alveolar permeability. Computed tomography scan revealed widespread infarctions in brain, spleen and kidneys, and pulmonary thromboembolism, suggesting the diagnosis of catastrophic antiphospholipid syndrome.     

Isotype-specific antibody responses to Haemonchus contortus in genetically resistant sheep

The kinetics of anti-Haemonchus antibody responses in serum and faecal extracts of pasture-reared, genetically resistant and random-bred sheep infected with Haemonchus contortus were examined using an isotype-specific ELISA. Anti-Haemonchus antibodies of IgA, IgG1, IgG2 and IgM isotypes were detected in serum and faecal extracts of both resistant and random-bred sheep after challenge infection. Serum IgG1 and IgA levels in resistant sheep were significantly higher than in random-bred sheep between 10 and 31 days after infection. However, there were no differences in IgG2 and IgM antibody responses between the two genotypes. Faecal antibody responses to H. contortus showed a clear genetic effect with resistant sheep exhibiting higher IgA levels throughout infection and higher IgG1 levels between 24 and 31 days after infection. Furthermore, serum IgG1 and IgA, and faecal IgA responses were negatively correlated with faecal egg counts in both genotypes on 17, 24 and 31 days after infection. Together, these results are taken to indicate that anti-parasite IgA and IgG1 antibodies may play an important role in genetically determined resistance of sheep to haemonchosis     

Structural and molecular specificity of antibody responses in mice immune to third stage larvae of Onchocerca volvulus

Immunization of mice with irradiated Onchocerca volvulus infective stage larvae (L3) has been demonstrated to confer protection against challenge infections with these larvae. Additionally, cytokine level measurements and cytokine depletion studies have shown that both IL-4 and IL-5 are important in generating a protective immune response against O. volvulus challenge infections, thus suggesting a dependency of protective immunity on IgG1, IgE and/or eosinophils. In the present study, we examined the humoral responses of immunized mice to O. volvulus L3 antigens. ELISA measurements of total serum antibody levels indicated that IgE was the only antibody isotype elevated in mice immunized with O. volvulus L3. IgM from immunized mice was the only isotype that recognized surface antigens on intact O. volvulus L3. IgG1, IgG3, IgE and IgA recognized internal parasite antigens on O. volvulus L3 frozen sections. Western blot analysis of L3 proteins showed that in serum from mice immunized with O. volvulus L3 IgG1, IgG2a/2b, IgA, and IgE, as well as IgM, recognized unique L3 proteins. Antibodies in serum from L3 immunized mice were able to detect O. volvulus adult antigens in a pattern similar to the recognition found in O. volvulus L3. Some L3 antigens were shared by adults, while other antigens were L3 specific. The ELISA, immunohistochemistry and Western blot findings thus demonstrate a complex pattern of antigen recognition of parasite antigens by antibodies found in mice immune to the L3 of O. volvulus     

Immunoglobulin class specific responses to biochemically defined antigens of Trichinella spiralis

A comparison of the humoral response to resistant (NIH) and susceptible (C3H) strains of mice, which reject adult worms at different rates during a primary infection, was made following infection with Trichinella spiralis. The serum concentration of immunoglobulins of the heavy chain classes IgM, IgG1, IgG2, IgG3 and IgA were determined by single radial immunodiffusion. Antibodies of the same immunoglobulin isotypes to biochemically defined, stage specific surface and secreted components of three stages of parasite development were also determined using an isotype specific immuno-coprecipitation assay. Independent variation of the responses of each immunoglobulin isotype was observed. The specific anti-parasite response did not reflect total serum immunoglobulin levels in all immunoglobulin classes, and this is discussed in relation to basic mechanisms of immunoglobulin class switching. Finally a close correlation was observed in resistant (NIH) mice between the production of IgA antibody to surface components of adult worms and accelerated expulsion of this stage of the worm from the gastrointestinal tract. The possible relevance of this IgA response is further indicated by the failure of susceptible mice to synthesise IgA antibodies to the same surface antigens.     

Diagnostic specificity of immunoglobulin M (IgM) response in differentiation Legionnaires' disease from psittacosis.

Specific IgM and IgG antibody responses to Legionella pneumophila (LDB) and Chlamydia psittaci (PSI) in serum specimens from 22 cases of Legionnaires' Disease (LD) were examined by micro-immunofluorescence (IF) tests to explore the diagnostic significance of the IgM antibody response. Serial samples from 5 patients with LD showed greater than or equal to 4-fold changes in IgG antibody against LDB and PSI. All 5 patients possessed IgM antibodies against LDB but not against PSI. In single convalescent serum samples from 17 additional cases, 16 exhibited IgG and 15 showed IgM antibodies against LDB; all 17 exhibited IgG but not IgM antibodies against PSI. The IgM antibody response appears more specific than the corresponding IgG response in the serodiagnosis of LD, and may be valuable in differentiating LDB infections from those due to PSI.     

Antibody isotype responses to the Schistosoma mansoni schistosomulum in the CBA/N mouse induced by different stages of the parasite life cycle

Summary During infection with Schistosoma mansoni the extent and nature of immune reactions against schistosomula may be influenced by responses to cross-reactive antigens in eggs or adult worms, and there is now extensive evidence for cross-reactivity between the different stages of the parasite life cycle. In this study IgM and IgG subclass antibodies produced in (CBA/N × Balb/c) Fl male and female mice were measured over a period of time following exposure to a chronic infection, to unisexual male cercariae or to irradiated larvae. Antibody levels were also measured following immunization with antigen preparations derived from adult worms, schistosomula or eggs. (CBA/N × Balb/c) Fl male mice exhibit an X-linked immune deficiency which results in an inability to respond to T-independent (TI) type 2 polysaccharides. Isotype levels were measured by ELISA to detergent-soluble schistosomulum antigen. Results showed that antigens on the different stages of the parasite life cycle have a qualitative influence on the antibody response to the larval surface, and that T-independent type 2 polysaccharides, particularly abundant in egg. exhibit antigen-directed isotype restriction in the form of IgM and IgG3 antibodies.