Single Radial Immunodiffusion Test Research Articles

Role of Innate Immunity in Patients with HBV Infection

Background: The hepatitis B virus [HBV] is an infectious disease and its one of the great public health problem, its outcome depends on the kinetics of the virus-host interaction and specifically on the strength of the innate and adaptive, humoral and cellular immune response. Thus interactions between the virus and the components of immune systems plays an important role in the pathogenesis of the disease. This study aimed to evaluate innate immune response in different clinical courses of HBV infection by estimation serum levels of granulocytemacrophagecolony stimulating factor (GM-CSF), Interleukin-1 (IL-1 ), Interleukin-8 (IL-8 ) , immunoglobulin A (IgA), IgM, IgG and Complement component (C3and C4) levels. Aim of study: to evaluate role of immune response in clinical course of hepatitis B infection Patients and Method: This study based on 78 patients with HBV infection attending the Public Health Laboratories. Their ages ranged from (14-65) years, (58 males and 20 females) compared with 20 healthy subjects (12 males and 8 females) as control group. This study extended from first of January 2015 to first of January 2017. The patients were classified to three groups on the bases of serologic markers (HBsAg, HBe Ag, HBc Ab IgM) according to WHO department of communicable disease surveillances and response, liver function tests which are used as supportive indicator for the liver injury, history of the illness, and full clinical assessment. The first group includes twenty-eight patients with acute HBV infection, second group include twenty cases identified as chronic healthy HBsAg carriers group and the last third group include thirty cases of chronic HBV group Results: By using enzyme immuno assay [ELISA] technique, serum levels of interleukin1alpha [IL-1α], interleukin-8 [IL-8], and granulocyte-macrophage-colony stimulating factor [GM-CSF] were measured in all patients compared to that of healthy control group. The mean levels of IL-1α and IL-8 showed a significant increase in serum of patients with newly infected (acute) HBV and chronic HBV compared with studied control group [P=0.04 and P=0.001 respectivel]. However, the mean serum levels for IL-1α and IL-8 recorded a non significant increase in patients with chronic healthy HBsAg carriers [P=0.17 and P=0.4 respectively]. While the mean serum levels of GM-CSF showed a significant rise in acute HBV only [P=0.01]. Moreover, serum immunoglobulins [IgG, IgM, IgA] and complement component [C3, C4] levels also evaluated by using single radial immunodiffusion test (SRID). The mean serum IgA, IgG and IgM levels showed a significant increase in chronic HBV group as compared to that of control group [ P=0.000 ,P=0.000 and P=0.001 respectively].. The mean serum C3 and C4 levels showed a significant lower serum level in all groups compared to control studied group [P=0.000]. Conclusion: this data demonstrate that immunological differences do exist between different clinical groups with HBV infection and may reflect the role of the innate immune system in host defense and disease

Brix refractometer scoring of immunoglobulin G in postpartum mares’ colostrum

Newborn foals are dependent on ingestion of high-quality colostrum for their immune protection. Colostrum quality (immunuoglobulin G [IgG]) can be determined by the single radial immunodiffusion (SRID) test or estimated by Brix refractometer. Goal was to compare SRID test findings (IgG concentrations) and Brix refractometer readings (IgG percentage) in colostrum samples collected from mares during the first 12 - 18 hours postpartum. A total of 56 colostrum samples were collected from 10 postpartum mares. Postfoaling, colostrum IgG concentrations were 21,785 ± 5,592 mg/dl and IgG percentage was 27.9 ± 3.7%. At 12 hours postfoaling, IgG concentrations decreased to 1,713.9 ± 1,380.4 mg/dl and its percentage to 11.4 ± 1.6%. There was a high correlation (r = 0.9661) between SRID test results and Brix refractometry scores. In summary, Brix refractometry can be used to monitor colostrum quality.

Evaluation of Brix Refractometry for the Estimation of Colostrum Quality in Jennies

Donkey placenta does not allow the passage of immunoglobulins; thus, foals are born hypogammaglobulinemic and an adequate intake of high-quality colostrum in the first 24 hours of life is crucial for the surviving. The study aims to assess the relation between colostrum immunoglobulin G (IgG) concentration evaluated by the single radial immunodiffusion (SRID) test and the Brix refractometer in donkeys to establish a cutoff value for high quality of colostrum based on Brix refractometry. Colostrum was collected at foaling, and at 6, 12, and 24 hours after foaling from the left and the right half of nine Amiata jennies. A total of 72 colostrum samples were analyzed. A Friedman test with a Dunn’s test for multiple comparisons was used for assessing the differences between the left and right half at each sampling time. No differences were found between the left and right halves; the average value was used to analyze the effect of sampling time on the IgG concentrations and Brix values. The relationship between colostrum IgG concentrations (SRID test) versus Brix value and Brix value versus time was analyzed using two different mixed linear models. A strong statistically significant relation has been found between IgG concentrations and Brix values (R2 = 0.84). The relation between IgG concentrations and Brix refractometer showed a cutoff point of 17% Brix score for the identification of high-quality colostrum. The Brix value (%) decreased continuously from 16.29 by 0.29 × hour. Jennies’ and donkey foals’ management may be greatly improved using this simple and cheap device.

STUDY OF SOME HUMORAL IMMUNITY PARAMETERS POST MICE IMMUNIZATION MICE WITH KLEBSIELLA PNEUMONIAE ATTENUATED WITH NATURAL PRODUCTS

Isolated and well identified K. pneumoniae, was included in this study the sensitivity to some antibiotics and the impact of certain natural products (honey and garlic) against these bacteria and Impact Statement synergistic action of these products with antibiotics, as the results showed that interference honey and garlic juice with antibiotics significant effect in increasing the sensitivity of the K. pneumoniae to antibiotics, and were grown K. pneumoniae in the nutrient broth containing different concentrations of honey and garlic juice, and tested the susceptibility for the same antibiotics mentioned. The isolation of K. pneumoniae is used in this study of humoral immune indicators. As a method is used Single Radial Immunodiffusion Test Kits to measure the levels of antibodies and complement proteins, the results showed a significant increase in the level antibodies types IgA, IgM, IgG and complement proteins C3, C4 for immunization groups compared with positive and negative control groups.

Correlation of Serum IgG Concentration in Foals and Refractometry Index of the Dam’s Pre- and Post-Parturient Colostrums: An Assessment for Failure of Passive Transfer in Foals

The object of this study was to evaluate the usefulness of measuring the differences in the values of the serum total protein (DVSTP) concentration of foals and the refractometry index (DVRI) of the milk of dams before and after nursing of the colostrum for assessing failure of passive transfer (FPT) in foals. Serum samples from 31 foals were collected before the first nursing and other 1 to 6 times between 4 and 24 hr after birth. Paired colostrum and milk samples were collected from 14 of their dams at the same time. Serum samples were analyzed for IgG concentration using a single radial immunodiffusion (SRID) test (98 samples) and total protein concentration using a temperature-compensating refractometer (98 samples). Colostrum and milk samples were analyzed for refractometry index (RI) using a Brix refractometer (71 samples). DVSTP concentration and DVRI were significantly correlated with serum IgG concentration. The negative predictive values (NPVs) of DVSTP concentration for detecting serum IgG concentrations<400 mg/dl and<800 mg/dl were 98.2% and 91.3% when the cutoff value is set to 0.4 mg/dl and 0.8 mg/dl, respectively. Furthermore, the NPVs of DVRI for detecting serum IgG concentrations<400 mg/dl and<800 mg/dl were 97.3% and 96.3% when the cutoff value is set to 6% and 10%, respectively. The results suggest that measurement of DVRI is useful in assessing FPT as an initial "stall-side" screening test, because it is easy, inexpensive to perform and allows for rapid interpretation.

Study on some predelivery immunoparameters in pregnant women in Al-Ramadi city

Serum Protein plays major role to maintain balance of blood, so total protein may be elevated or decreased due to some pathological & physiological changes in human body during pregnancy period. On the other hand the serological diagnosis of antibodies level during pregnancy is usually based on the detection of IgG and IgM antibodies as markers for diagnosis. The aim of this study was to investigate some immunoparameters including IgM, IgG, and assay of TSP, TSA & TSG in pregnant women attending Maternity & Child Hospital in Ramadi City, West of Iraq. Sera of 50 pregnant women were collected & quantitative assays by Single Radial Immunodiffusion test (Mancini test) for detection of (IgM & IgG) concentration & spectrophotometric method for Total serum protein, Total serum Albumin & Total serum Globulin reader were achieved against these serum samples.Serum immunoglobulin (IgM & IgG) were measured in 50 pregnant women. (22) with natural delivery & (28) Cesarean delivery pregnant women. The mean IgG level was increased in pregnant women aged under 25 years, while IgM levels were markedly increased at (25-39) years. A total mean titer for IgG & IgM were found to be 1006.2071± 408.12282 & 48.8571±28.81962 respectively.Total serum protein reports separate values for total protein , albumin & Globulin. Values of serum protein reflect high globulin concentration, while albumin concentration in pregnant women recorded significant differences It is mean values for age group (15-24) & (25- 39) years are 3.4479 ± .72373 & 3.0044±.33212 respectively. There was significant differences in albumin concentration through age group in pregnant women. Most values of serum routine liver function tests during normal pregnancy remain below the upper normal limits in no pregnant women. When liver disease is suspected & considered pathologic further should prompt evaluation. Furthermore, IgG concentration was predominantly increase in their level during pregnancy in association with transported IgG through placenta to the fetus during late pregnancy period

Serum α‐1‐acid glycoprotein concentrations in 26 dogs with pyometra

The acute phase protein, α-1-acid glycoprotein (AGP), has been proposed to have a role in immunomodulation and to be a nonspecific antimicrobial agent. We suggest that AGP may be increased in dogs with pyometra and possibly to a greater extent in dogs also manifesting signs of systemic inflammatory response syndrome (SIRS). Our objectives were to evaluate serum AGP concentrations in dogs diagnosed with pyometra compared with clinically healthy female dogs and to determine if AGP concentrations were correlated with severity of disease. Twenty-six dogs with pyometra and 18 clinically healthy intact female dogs were included in this prospective study. A diagnosis of pyometra was verified by histopathologic examination after ovariohysterectomy in the pyometra group. A commercially available single radial immunodiffusion test was used for AGP analysis. Clinical findings, laboratory variables, and hospitalization times were compared. Mean AGP concentration in dogs with pyometra (1943 ± 913 mg/L, mean ± SD), was significantly higher (P<.001) than in healthy dogs (495 ± 204 mg/L). Mean AGP concentration in dogs in the pyometra group with (n=18) or without (n=8) SIRS did not differ. Animals with a prolonged hospital stay had higher AGP concentrations. Pyometra was associated with increased serum concentrations of the acute phase protein AGP. AGP concentrations were associated with severity of disease as measured by duration of hospitalization. As AGP binds basic drugs, further studies of its pharmacokinetic and pharmacodynamic propreties in cases of pyometra may be of clinical interest.

Complement C3 in Bernese Mountain dogs

Previous research suggests that low serum concentrations of the third component of complement (C3) are associated with both the susceptibility to infectious agents such as Borrelia burgdorferi and the development of glomerular disease. We hypothesized that low levels of C3 are associated with the coincident occurrence of B. burgdorferi infection and glomerulonephritis in Bernese Mountain dogs. The aims of this study were to evaluate the serum concentration of C3 in Bernese Mountain dogs with and without antibodies against B. burgdorferi and to compare this concentration with that of healthy control dogs. Eighty-three clinically healthy Bernese Mountain dogs and 46 control dogs were included. Antibodies against B. burgdorferi were determined using an ELISA with a whole cell sonicate as antigen. Results were confirmed using Western blot. C3 was measured using a single radial immunodiffusion test. Results were reported as the percentage concentration of C3 compared with that in pooled preserved canine serum (100% C3 concentration). Median C3 concentration was 128.5% in Bernese Mountain dogs with antibodies against B. burgdorferi, 133.5% in B. burgdorferi-negative Bernese Mountain dogs, 87.8% in positive control dogs, and 102.2% in negative control dogs. Within Bernese Mountain and control groups, C3 was lower in dogs with antibodies against B. burgdorferi compared with those without. Percentage concentration of C3 was higher in healthy Bernese Mountain dogs compared with control dogs. Low C3 concentration is not an explanation for the high prevalence of B. burgdorferi infections and glomerular disease in Bernese Mountain dogs.

A novel positive regulatory element for exfoliative toxin A gene expression in Staphylococcus aureus.

A 1.4 kb positive regulatory element (ETA(exp)) that controls staphylococcal exfoliative toxin A (sETA) transcription was cloned from Staphylococcus aureus. ETA(exp) is located upstream of the cloned 5.8 kb eta gene (etaJ1) obtained from the chomosomal DNA of S. aureus ZM, the standard ETA-producing strain. The cETA prepared from an Escherichia coli transformant into which the recombinant plasmid petaJ1 (5.8 kb eta/pUC9) had been introduced was expressed at high levels in the culture supernatant and the ammonium-sulfate-precipitated culture supernatant fraction as shown by immunoblotting and the single radial immunodiffusion test. However, cETA produced by the recombinant plasmid petaJ3 containing the 1.7 kb eta sequence (etaJ3) with a 1.45 kb ETA(exp)-deficient eta fragment (1.7 kb eta/pUC9) obtained from the 5.8 kb eta sequence by subcloning was not detected in either the culture supernatant or the ammonium-sulfate-precipitated culture supernatant fraction (167-fold concentrate of the culture supernatant) by immunoblotting or the single radial immunodiffusion test. A large amount of cETA was produced by the 1.7 kb eta sequence when it was linked to ETA(exp) amplified by PCR (1.7 kb eta-ETA(exp)/pUC9), regardless of the orientation of ETA(exp) insertion. Northern blot hybridization showed lower levels of the transcripts of the 1.7 kb eta sequence than of the 5.8 kb eta sequence. The rsETA prepared from an S. aureus transformant into which the recombinant plasmid 3.4 kb eta-ETA(exp)/pYT3 (pYT3-etaJ6) had been introduced was expressed at high levels in the culture supernatant fraction as shown by the latex agglutination test. However, the agglutination titre in the culture supernatant fraction of rsETA produced by the recombinant plasmid (1.7 kb eta/pYT3) containing the 1.7 kb eta sequence carrying the 1.4 kb ETA(exp)-deficient eta fragment (pYT3-etaJ3) was 2500-4000 times lower than that of pYT3-etaJ6.

Lactoferrin concentrations in milk from normal and subclinical mastitic cows.

The concentrations of lactoferrin (Lf) in quarter milk from normal lactating cows and subclinical mastitic cows were measured to determine whether the Lf concentration in milk is influenced by the age of the cow, the stage of lactation, number of milk somatic cells and the presence of pathogens. Lf concentrations in 111 quarter milk samples from 28 normal lactating cows and 270 quarter milk samples from 198 subclinical mastitic cows were measured by means of a single radial immunodiffusion test. Lf concentrations (means +/- standard deviations; logarithmic form) in normal cows and subclinical mastitic cows were 2.23 +/- 0.39 and 2.70 +/- 0.39, respectively. The mean milk Lf concentration (log) in subclinical mastitic cows was significantly (p<0.01) higher than that in normal cows. The mean milk Lf concentration (log) in normal lactating cows aged 5 years was lower than those in normal lactating cows aged 2 years (p<0.01) and 3 years (p<0.05). The results showed that the milk Lf concentration (log) is associated with age of the dairy cow (one-way analysis of variance test, p<0.01). The mean milk Lf concentration (log) in the latter lactational period tended to be higher than those in the peak and middle periods. Milk Lf concentrations (log) tended to be proportional to the level of the somatic cell count (SCC) score. Mean milk Lf concentrations (log) in subclinical mastitic cows infected with Staphylococcus aureus and with other streptococci species were significantly (p<0.01) higher than those in cows infected with coagulase-negative staphylococci and with Corynebacterium bovis.

Evaluation of the SNAP Foal IgG test for the semiquantitative measurement of immunoglobulin G in foals

The SNAP Foal IgG test (IDEXX) as evaluated for its accuracy and usefulness by measuring blood samples collected from 42 foals between 24 and 48 hours after birth. The results...

Some properties of nickedVibrio vulnificushemolysin

Vibrio vulnificus, an opportunistic human pathogen, secretes the 50 kDa single-chain hemolysin. When incubated with an exocellular protease from this vibrio, the 50 kDa hemolysin was cleaved in some peptides joined with the disulfide bond(s); the 40 kDa fragment and the small fragment(s) undetectable in SDS-PAGE. The nicked hemolysin induced comparable hemolysis through the same process as that of the intact toxin. However, the nicked hemolysin was found to be more stable against inactivation due to autoaggregation, so that it formed a larger precipitation zone in the single radial immunodiffusion test using the antiserum against the intact hemolysin. These results suggest thatV. vulnificushemolysin is modified to be a more hydrophilic protein by nicking, while it is not accompanied by loss of the hemolytic activity.

Development of a New Quantitation Test for Horse IgG Using Nephelometry and Clinical Application of the Test.

An easily performed test that can provide accurate, rapidly available results for quantitation of horse IgG has been developed using nephelometry. This test is expected to be used for diagnosis of such immunological diseases as failure of passive transfer of colostral immunoglobulin from mares, which is the most common immunodeficiency disorder in foals. Correlation coefficient and p value among results for single radial immunodiffusion test and the nephelometry in 58 half-bred horses were 0.850 and < 0.0005. The test was applied to quantitation of serum IgG from 100 race horses. The mean value was 1, 603 mg/dl, with a standard deviation of 294.8 mg/dl, a minimum value of 1, 004 mg/dl, and a maximum value of 2, 391 mg/dl. The test was also utilized to clinical practice in a farm. A relationship between IgG quantity at seven days after birth and the period from birth to the first day of therapy for clinical illness was observed for 16 foals of a farm until 180 days after birth. The IgG quantities at seven days after birth was 140 to 1, 700 mg/dl, and 12 foals were treated for common cold, bronchitis or pneumonitis within 135 days after birth. This result suggested that foals have the same possibility for clinical illness, regardless of their IgG quantities at seven days after birth. However, treated foals with lower IgG quantities tended to show clinical illness earlier after birth.

Sandwich enzyme-linked immunosorbent assay for quantitative measurement of serum amyloid A protein in horses

SUMMARY To measure the concentration of serum amyloid A (saa) protein in horses, a sensitive and highly reproducible sandwich (elisa) was established, using affinity purified saa antibody. Results of the elisa were found to have a high correlation (r = 0.95) with those of the single radial immunodiffusion test. Equine saa concentration was measured by use of this elisa. In clinically normal horses, the concentration of saa was high immediately after birth to 2 weeks of age. After that, saa concentration had periodic fluctuations in the range of approximately 10 to 30 μg/ml. Mean (± sd) concentrations of saa in foals (≤ 12 months old) and adult horses (≥ 18 months old) were 21.23 ± 12.20 and 14.93 ± 9.07 μg/ml, respectively. In mares during the perinatal period, saa concentration remained stable within the reference range before parturition. It increased quickly after delivery, and reached a peak value of 101.29 ± 98.82 μg/ml on postpartum day 3, then began to decrease, at postpartum week 2, to the reference range by the end of postpartum month 1. In horses with experimentally induced inflammation, saa concentration increased quickly and reached approximately four- to 40-fold increase over the pretreatment value on day 1 and remained high on days 2 to 6 after treatment. It then returned to the baseline value by 2 to 4 weeks in association with disappearance of local signs of inflammation. The saa concentration was high in most horses with clinical signs of inflammation. It was concluded from these data that this elisa is sensitive and reliable for measuring saa in horses.

Immunologic studies of a horse with lymphosarcoma

Immunological, clinical, and pathological investigations were conducted on a horse with lymphosarcoma. The immunological status was investigated by measuring the level of antibodies by single radial immunodiffusion test and the ability of lymphocytes to proliferate in response to mitogens. Multiple immunological abnormalities were noted in this horse. They were; (1) decreased IgM, IgG, and IgA levels in the serum despite hyperproteinemia; (2) increased in-vitro spontaneous lymphoproliferation which reflects augmented mitosis; (3) decreased lymphoproliferative response to T cell stimulants (e.g. Concanavalin-A (Con-A)) suggesting impaired T cell activation; (4) presence of immunosuppressive factors in serum as demonstrated by in-vitro lymphocyte culture systems. Clinical pathology findings revealed an unusual monoclonal α peak in the serum and morphologically abnormal lymphocytes distributed throughout the body. Serum fractionated by fast protein liquid chromatography (FPLC) revealed that the immunosuppressive factors were found in this abnormal α peak. The immunopathological findings in this horse are discussed.

A study of bovine and equine immunoglobulin levels in pony foals fed bovine colostrum

As part of a project to raise specific pathogen free (SPF) Welsh Mountain Pony foals, free from exposure to Equid herpesvirus type 1, foals were removed from their dams at birth and fed bovine colostrum. This study characterises the uptake of bovine colostral immunoglobulin and production of endogenous immunoglobulin, in 10 SPF foals. An enzyme-linked immunoadsorbent assay was developed to measure serum concentrations of bovine IgG1 (boIgG1) to assess the efficiency of transfer, and rate of elimination of boIgG1 by the foal. The endogenous production of equine IgG was studied using a single radial immunodiffusion test. Foals were given 1.2 to 2 litres of bovine colostrum achieving peak serum boIgG1 concentrations of 18.9 to 34.2 g/litre (mean 28.0). The mean half-life of boIgG1 in the foals was 7.4 days. Endogenous immunoglobulin production resulted in equine IgG concentrations greater than 2 g/litre in six of 10 foals by 14 to 19 days of age, and greater than 7 g/litre in eight of 10 foals by 37 to 50 days of age. All foals had equine IgG serum concentrations greater than 10 g/litre by 102 to 135 days of age.

Comparison of Lactoferrin Content in Colostrum Between Different Cattle Breeds

Lactoferrin content of colostrum obtained from cows within 24h after parturition was measured using a single radial immunodiffusion test and was compared among cows of two dairy breeds (Holstein-Friesian, Jersey) and two beef breeds (Japanese Black and Japanese Brown). Average lactoferrin content in colostrum of dairy breeds was 2 mg/ml and in colostrum of beef breeds was .5 mg/ml. Lactoferrin content of colostrum due to lactation number was also different among breeds. In dairy breeds, multiparous cows had lactoferrin content two to three times higher than that of primiparous cows; beef breeds showed no obvious differences between lactation years. Lactoferrin content also varied considerably within breed. In beef breeds, half the cows had values of nearly zero. Transferrin content in colostrum was fairly constant (.9 mg/ml) and was not as variable among and within breeds. There was no correlation between lactoferrin and transferrin contents in colostrum. Examination of cows lacking lactoferrin suggested that transferrin plays an important role as an iron carrier from a cow to her newborn calf.

A modification of the single radial immunodiffusion potency test (SRD) for rabies vaccines

In 1983 a WHO collaborative study showed that the single radial immunodiffusion test provided a reliable system for the assay of the glycoprotein content of inactivated rabies vaccines. We have modified the method used in the collaborative study by using round plastic plates with wells arranged in a circle. Potency estimates were made by the multiple slope ratio method and not by single slope estimation procedures adjusted for a common intercept. We carried out a statistical evaluation of the accuracy and reliability of the precipitation area calculation. We confirmed that for the purpose of the potency estimation the area calculations were sufficiently precise in most instances. By analysing the sources of variation for round and for glass plates and by testing the variability of these methods we found that the round plates were as good as the glass plates. The advantage of the round plates was mainly in the ease of their handling: the agarose solution was poured in the plates without the need for a separate mould; an integral moist chamber with these plates was readily available; the precipitation zones were measured easily using a viewer which gave fourfold enlargements and the method required less antiglycoprotein.

NIH test, a problematic method for testing potency of inactivated rabies vaccine

A critical review of the NIH test is given. The results of four studies are presented which show that in the case of purified chick embryo cell inactivated rabies vaccine there is a profound difference between the result after heterologous intracerebral challenge with the prescribed CVS strain and homologous challenge with the LEP-C 26 strain. CVS strains from various laboratories produced relatively uniform results following intracerebral administration. Two in vitro tests, the single radial immunodiffusion test and the modified antibody binding test were employed in the studies. The results are discussed and alternative procedures to the NIH test are recommended for future consideration.

Serum antibody and cellular responses in LEW and F344 rats after immunization with Mycoplasma pulmonis antigens.

Mycoplasma pulmonis causes a chronic respiratory disease in rats which is more severe in LEW than in F344 rats. This study compared the ability of each of these rat strains to produce specific immune responses to M. pulmonis antigens. By an enzyme-linked immunosorbent assay, LEW rats were found to produce approximately 10 times lower levels of specific immunoglobulin G (IgG) after immunization with M. pulmonis antigens than F344 rats, while no significant difference was found in the levels of IgM. The difference in IgG levels was due to much greater levels of specific IgG2b (about 50 times) in F344 rats; no differences were found in other subclasses. Nonimmune LEW rats were found to have as much total IgG2b in their sera as unimmunized F344 rats by a single radial immunodiffusion test; thus, the difference was not due to the inability of LEW rats to produce IgG2b. In contrast to the antibody response to M. pulmonis antigens, anti-keyhole limpet hemocyanin IgG responses in LEW and F344 rats were similar, but F344 rats produced significantly more (about 21 times) IgG2b than was found in M. pulmonis responses. Antisera from F344 rats recognized several additional M. pulmonis antigens than antisera from LEW rats; however, this could not explain the differences in the level of IgG2b in LEW and F344 rats. In vitro stimulation of splenic lymphocytes with M. pulmonis antigens from immunized F344 rats produced much greater proliferative responses than in LEW and nonimmune F344 cells. Thus, the susceptible rat strain LEW produced lower cellular and humoral immune responses to M. pulmonis antigens than the resistant rat strain F344 after immunization.