Effect of Sinorhizobium meliloti lipopolysaccharide on blood cell composition in experiment

2019 ◽  
pp. 20-28
Author(s):  
А.Р. Мавзютов ◽  
Р.Р. Гарафутдинов ◽  
А.Р. Габдрахманова ◽  
И.М. Салахов ◽  
И.Д. Тупиев
Keyword(s):  
Single Dose ◽  
Bacterial Infections ◽  
Sinorhizobium Meliloti ◽  
White Blood Count ◽  
Immunodeficient Mice ◽  
Group 3 ◽  
Group 2 ◽  
Emergency Myelopoiesis ◽  
Hematopoietic Activity ◽  
Group 1

Липолисахариды (ЛПС, эндотоксины) грамотрицательных бактерий обладают выраженной биологической активностью, в том числе терапевтической, однако для S. meliloti таких данных нет. Цель работы - экспериментальное изучение гемопоэтической активности 4 фракций липополисахаридов, выделенных из S. meliloti, при индуцированном иммунодефиците у мышей. Методика. Сформировано 7 групп лабораторных мышей (по 10 особей в каждой): 1-я группа - интактные (контроль 1), 2-я - 7-я группа - мыши с иммунодефицитным состоянием, индуцированным однократным внутрибрюшинным введением циклофосфамида. Через 1 сут после моделирования иммунодефицита в течение 21 сут ежедневно мышам 3-й группы вводили препарат сравнения Ликопид® (химическое название: [4-O-(2-ацетиламино-2-дезокси-β-D-глюкопиранозил)-N-ацетилмурамил]-L-аланил-D-α-глутамиламид - синтетический аналог бактериальных гликопептидов из группы иммуностимулирующих средств). Мышам 4-7-й групп - вводили исследуемые фракции липолисахаридов - ЛПС-1, ЛПС-2, ЛПС-3 и ЛПС-4 соответственно. Для ликопида разовая доза составляла 0,1 мл (0,05 мг/мл), для исследуемых фракций ЛПС S. meliloti - 0,2 мл (10 пг/мл). Иммунодефицитным мышам 2-й группы фракции липополисахаридов и препарат сравнения Ликопид® не вводили Через 21 сут мышей выводили из эксперимента. Изучали весовые характеристики органов подопытных животных и лейкоцитарную формулу. Результаты. Введение мышам на фоне вторичного экспериментального иммунодефицита ликопида сопровождалось снижением количества палочкоядерных нейтрофилов и моноцитопенией; при введении фракции ЛПС-1 возрастало количество сегментоядерных нейтрофилов; ЛПС-2 - имели место снижение содержания палочкоядерных нейтрофилов и лимфоцитоз; ЛПС-3 - наблюдали снижение содержания палочкоядерных нейтрофилов и лимфоцитоз на фоне значимого увеличения количества сегментоядерных нейтрофилов; ЛПС-4 - констатировалось увеличение числа базофилов, снижение содержания палочкоядерных нейтрофилов и лимфоцитоз на фоне значимого увеличения количества сегментоядерных нейтрофилов. Заключение. Фракции ЛПС Sinorhizobium meliloti проявляют модулирующие эффекты, схожие с механизмами «экстренного миелопоэза» при физиологичном варианте течения бактериальных инфекций. Lipolysaccharides (LPS, endotoxins) of gram-negative bacteria have a pronounced biological activity, including therapeutic activity; however, there is no such data for S. meliloti. Aim. To conduct an experimental study of hematopoietic activity of four lipopolysaccharide fractions isolated from S. meliloti under induced immunodeficiency in mice. Methods. 7 groups of 10 laboratory mice each were formed: group 1, intact mice (control 1); groups 2-7, mice with immunodeficiency induced by a single intraperitoneal injection of cyclophosphamide. Mice of group 3 were daily injected with a comparison agent, Licopid® (Chemical name: [4-O- (2-acetylamino-2-deoxy-β-D-glucopyranosyl) -N-acetylmuramyl] -L-alanyl-D-α-glutamyl amide; single dose, 0.1 ml (0.05 mg/ml)) for 21 days starting one day after the induction of immunodeficiency. Mice of groups 3-7 were injected with the studied S. meliloti LPS fractions, LPS-1, LPS-2, LPS-3, and LPS-4, respectively (single dose, 0.2 ml (10 pg/ml)). Immunodeficient mice of group 2 received neither the comparison agent, Licopid® nor LPS fractions. The mice were euthanized at 21 days. Weight characteristics of animal organs and white blood count were studied. Results. Administration of Licopid® to mice with secondary experimental immunodeficiency was associated with decreased count of stab neutrophils and monocytopenia; LPS-1 fraction increased the count of segmented neutrophils; LPS-2 decreased the count of stab neutrophils and induced lymphocytosis; LPS-3 decreased the count of stab neutrophils and induced lymphocytosis associated with a significant increase in the count of segmented neutrophils; LPS-4 induced basophilia, decreased count of stab neutrophils, and lymphocytosis associated with a significant increase in the count of segmented neutrophils. Conclusion. Sinorhizobium meliloti LPS fractions exerted modulating effects similar to the mechanisms of “emergency myelopoiesis” in the physiological course of bacterial infections.

scholarly journals Anti-CD28 Monoclonal Antibody Therapy Prevents Chronic Rejection of Renal Allografts in Rats

2002 ◽  
Vol 13 (2) ◽  
pp. 519-527
Author(s):  
Igor A. Laskowski ◽  
Johann Pratschke ◽  
Markus J. Wilhelm ◽  
Victor M. Dong ◽  
Francisca Beato ◽  
...  
Keyword(s):  
Single Dose ◽  
T Cell ◽  
Chronic Rejection ◽  
Interstitial Fibrosis ◽  
Inflammatory Factors ◽  
Renal Allografts ◽  
Short Course ◽  
Group 3 ◽  
Group 2 ◽  
Group 1

ABSTRACT. The effects of a signaling anti-CD28 mAb (JJ319), which interferes with the CD28-B7 T cell costimulation pathway thought to be involved in the development of chronic rejection of organ transplants, was investigated. Functional, morphologic, and molecular changes in rat renal allografts were examined up to 24 wk after placement. Control Lewis rats, recipients of F344 kidneys, received a single dose of a nonspecific mouse mAb intravenously on the day of transplantation (group 1). Group 2 animals were given anti-CD28 mAb in similar fashion. Group 3 animals were treated with a short course of cyclosporin A (CsA), and group 4 received both anti-CD 28 mAb and CsA. The majority (>95%) of animals in groups 2, 3, and 4 survived throughout the follow-up, compared with 28% in group 1 (P < 0.001). Group 2 and 4 recipients produced negligible proteinuria, whereas group 1 controls developed progressively increasing proteinuria after 4 wk and group 3 animals developed proteinuria by 24 wk. Allografts in groups 2 and 4 were morphologically unremarkable at 24 wk. Kidneys of group 1 animals rapidly developed changes of acute rejection, and those that survived long-term showed extensive glomerulosclerosis and interstitial fibrosis. Changes of early chronic rejection were noted in group 3 grafts. By reverse transcriptase–PCR, expression of representative inflammatory factors interferon-γ and interleukin-10 were significantly elevated at 24 wk only in the surviving group 1 animals. A single dose of a signaling anti-CD28 mAb administered at transplantation or in combination with a short course of CsA significantly prolonged recipient survival, normalized function, and preserved the morphology of renal allografts in an established model of chronic rejection. These data support an important role for T cell costimulation in the evolution of the chronic process.

Clinical outcomes of single-dose cardioplegia in high-risk coronary bypass

2020 ◽  
pp. 021849232096643
Author(s):  
Serdar Gunaydin ◽  
Orhan Eren Gunertem ◽  
Seyhan Babaroglu ◽  
Atike Tekeli Kunt ◽  
Kevin McCusker ◽  
...  
Keyword(s):  
Single Dose ◽  
Coronary Artery ◽  
High Risk ◽  
Myocardial Protection ◽  
Artery Bypass ◽  
Bypass Grafting ◽  
Risk Patients ◽  
Group 3 ◽  
Group 2 ◽  
Group 1

Background Despite the increasing popularity of single-dose cardioplegia techniques in coronary artery bypass grafting, the time window for successful reperfusion remains unclear. This study aimed to compare different cardioplegic techniques based on early and 30-day clinical outcomes via thorough monitoring. Methods This prospective cohort study included high-risk patients undergoing coronary artery bypass grafting and receiving 3 different types of cardioplegia between January 2017 and June 2019. Group 1 ( n = 101) had a single dose of del Nido cardioplegia, group 2 ( n = 92) had a single dose of histidine-tryptophane-ketoglutarate, and group 3 ( n = 119) had cold blood cardioplegia. Patients were examined perioperatively by memory loop recording and auto-triggered memory loop recording for 30 days, with documentation of predefined events. Results Interleukin-6 and cardiac troponin levels in group 1 were significantly higher than those in groups 2 and 3. The incidence of predefined events as markers of inadequate myocardial protection was significantly higher group 1, with more frequent atrial fibrillation attacks and more hospital readmissions. The readmission rate was 17.6% in group 1, 9% in group 2, and 8% in group 3. Conclusions Our data demonstrate the long-term efficacy of cardioplegic techniques, which may become more crucial in high-risk patients who genuinely have a chance to benefit from adjunct myocardial protection. Patients given del Nido cardioplegia had a significantly more prominent inflammatory response and higher troponin levels after cardiopulmonary bypass. This group had issues in the longer term with significantly more cardiac events and a higher rehospitalization rate.

scholarly journals AB1022 PANNICULITIS IN RHEUMATOLOGICAL PRACTICE: THE RESULTS OF LONG-TERM FOLLOW-UP

2020 ◽  
Vol 79 (Suppl 1) ◽  
pp. 1803.1-1804
Author(s):  
O. Egorova ◽  
B. Belov
Keyword(s):  
Bacterial Infections ◽  
Inflammatory Diseases ◽  
Subcutaneous Fat ◽  
Weight Lifting ◽  
Group 4 ◽  
Group 3 ◽  
Anti Inflammatory ◽  
Group 2 ◽  
Group 1

Background:Panniculitis is a group of heterogeneous inflammatory diseases that occur with damage to the subcutaneous fat (SCF), musculoskeletal system, and often internal organsObjectives:to evaluate the course and outcome in patients with panniculitisMethods:the course of the disease was monitored in 193 patients treated at the V.A. Nasonova Research Institute of Rheumatology for 3-5 years (142 women, 51 men) aged 19 to 77 with the referral diagnosis of erythema nodosum (EN) and undifferentiated panniculitis and with the disease duration of 1 week to 13 years. In addition to general clinical study, serum concentrations of α-1 antitrypsin, amylase, lipase, ferritin, creatinephosphokinase were determined, computed tomography of the chest organs, immunological, ultrasound scanning of the skin and SCF of the node area, tuberculosis tests and pathomorphological study of skin biopsy from the node area were performed.Results:: as a result of laboratory and instrumental examination, the following diagnoses were made: EN associated with infection (72 people – group 1), lipodermatosclerosis (LDS) (40 –group 2), idiopathic lobular panniculitis (ILP) (32 – group 3), Löfgren’s syndrome (SL) (49 –group 4). During the follow-up period, 6 deaths occurred (3.1%): in a patient with LDS due to acute heart failure and in 5 patients with ILP due to the activity of the disease which led to the development of cardiopulmonary pathology and disseminated intravascular coagulation (DIC) syndrome. In group 1, during the observation period, UE recurred in 18 people (25%), the probable causes were: hypothermia (6), exacerbation of chronic tonsillitis (6), acute respiratory viral infections (ARVI) (4), stress (1), a rapid decrease in the dose of glucocorticoids (GC) (1), the cause is unknown (2). In group 2, recurrence occurred in 19 patients (47.5%) due to the lack of anti-inflammatory therapy (plaquenil) (10), trauma (4), stress (3), and weight lifting (2). There was no recurrence in 7 patients in this group, however, nodes would not disappear completely, which is obviously due to the absence of plaquenil. In group 3, recurrence was registered in 24 cases (75%) and it was associated with insufficient effect of the ongoing anti-inflammatory therapy (9), a decrease in blood glucose to minimal doses (6), hypothermia (6) and the absence/cancellation of anti-inflammatory therapy (3). In group 4, recurrence of nodes was registered in 14 cases (28.5%), possible causes: cancellation of GC (9) and cooling/ARVI(5).Conclusion:in the observed group of patients with panniculitis mortality was 3.1%. The main causes of recurrence in EN were viral-bacterial infections, and in case of ILP, LDS and SL it was insufficient effect/absence of anti-inflammatory therapy.Disclosure of Interests:None declared

scholarly journals EFEK PENYUNTIKAN PROSTAGLANDIN F2α (PGF2α) TERHADAP TIMBUL DAN LAMA BIRAHI SAPI BALI PADA PARITAS YANG BERBEDA

2019 ◽  
Vol 44 (2) ◽  
pp. 141
Author(s):  
Abdul Malik
Keyword(s):  
Single Dose ◽  
Prostaglandin F2α ◽  
Estrus Synchronization ◽  
Group 4 ◽  
Significant Difference ◽  
Group 3 ◽  
Estrus Response ◽  
Group 2 ◽  
Time Required ◽  
Group 1

The objective of this study was to evaluate of Effect of injection Prostaglandin F2α on the time required for onset of estrus and estrus durations in Bali cattle with differences of Paritas. A total of 24 Bali cows were divided into four groups, each group was consisting of 6 cows.  Group 1 samples is heifer’s, group 2, samples was paritas1, group 3, samples was paritas 2 and group 4, samples was paritas 3.  All  cows were normal  tract of reproduction  with showing regular cyclic activities and having active of corpus luteum. The parameters in this study were determined including the time required for onset of estrus and duration of estrus. The result showed that percentage estrus response and duration of estrus were non-significant difference (P>0.05) between heifers and paritas 1, 2, and 3 after estrus synchronization with single dose of prostaglandin F2α. It was concluded that injection of PGF2α on heifers and Paritas 1,2 and 3 were  similar result on the time required for onset of estrus and duration of estrus.

scholarly journals Protective effect of Apelin-13 in a cyclophosphamide-induced cardiorenal toxicity model in rats.

2021 ◽  
Author(s):  
Özden Kutlay ◽  
Arzu Keskin-Aktan ◽  
Esra Aslan
Keyword(s):  
Single Dose ◽  
Protective Effect ◽  
Therapeutic Agent ◽  
Cardiac Toxicity ◽  
Antioxidant Properties ◽  
Control Group ◽  
Group 4 ◽  
Group 3 ◽  
Group 2 ◽  
Group 1

Cyclophosphamide is a chemotherapeutic drug that is widely used in the clinic and can cause multi-organ toxicity. Apelin-13 is an endogenous adipocytokine with antioxidant properties. Therefore, this study aimed to investigate the possibility of apelin-13 being a potential therapeutic agent on cardiac toxicity and nephrotoxicity caused by cyclophosphamide. In this study, a total of 4 groups were formed, including 8 rats in each group. Group 1: The control group was administered only saline (ip). Group 2: Cyclophosphamide, a single dose of 200 mg/kg (ip) on day 7. Group 3: Apelin-13 (15 μg/kg), for 7 days (ip). Group 4: Administering apelin-13 (15 μg/kg) (ip) for 7 days and a single dose of cyclophosphamide (200 mg/kg) (ip) on day 7, the rats were sacrificed on day 8. LDH, cTn1, cK-Mb, AST, ALT, ALP, MDA, creatinine, and BUN were found to be high in the cyclophosphamide group, however, these values were reduced with apelin-13 administration. Antioxidant enzymes such as SOD, GPx, CAT, and GSH decreased in the cyclophosphamide group, apelin-13 increased these enzyme activities. In addition, histopathological examinations also supported the results obtained. The findings of this study showed that apelin-13 has a protective effect against cardiorenal toxicity caused by cyclophosphamide.

scholarly journals A novel approach in non-surgical management of tubal ectopic: combination of minimally invasive technique under ultrasound guidance with systemic methotrexate based on initial beta-HCG levels

2021 ◽  
Author(s):  
Mayoukh Kumar Chakraborty ◽  
Shalini Gainder ◽  
Subhas Chandra Saha ◽  
Rashmi Bagga
Keyword(s):  
Single Dose ◽  
Ectopic Pregnancy ◽  
Success Rate ◽  
Surgical Management ◽  
Dose Regimen ◽  
Ultrasound Guided ◽  
Group 3 ◽  
Group 2 ◽  
Β Hcg ◽  
Group 1

Background: Single dose methotrexate is the most preferred method of non-surgical management of unruptured tubal ectopic. A 2-dose regimen is suggested to treat tubal ectopic with higher trophoblastic cell load. Minimally invasive technique of ultrasound guided intracardiac KCL instillation along with systemic methotrexate has been in use even for live ectopic pregnancy. Objective of the study was to evaluate the success rate of single dose regimen of MTX (Methotrexate), 2-dose regimen of MTX and ultrasound guided instillation of intracardiac KCl in three different cohort of unruptured tubal ectopic pregnancy with an attempt to increase success of non-surgical management.Methods: Fifty-eight women with unruptured tubal ectopic pregnancy were assigned to treatment protocols according to the initial β-HCG levels and presence/absence of FCA (fetal cardiac activity). Group 1: presence of FCA in the tubal ectopic; Group 2: initial β-HCG ≤5000 IU/ml; Group 3:  initial β-HCG ≥5000 IU/ml without FCA. Women in group 1 were treated with ultrasound guided instillation of intracardiac KCl combined with systemic MTX. While women in group 2 were administered single dose regimen of MTX and group 3 received 2-dose regimen of MTX.Results: Overall success rate of non-surgical management was 89.3% across all groups. Success rate in Group 1 was 78.6%. Success rate was 93.1% in group 2 while 92.3% in group 3. Rupture rate was 1.7% in the present study.Conclusions: For non-surgical management categorizing and treating is an option with good result. Women with presence of cardiac activity can opt for non-surgical option with likely resolution in 78% cases.

scholarly journals Evaluation of serum procalcitonin as a significant marker in cases of septic arthritis and osteomyelitis: a two year study

2018 ◽  
Vol 4 (4) ◽  
pp. 601
Author(s):  
Harsha Kumar Koramutla ◽  
Balakondaiah Koyagura ◽  
Bijju Ravindran
Keyword(s):  
Septic Arthritis ◽  
Bacterial Infections ◽  
Specific Marker ◽  
Predictive Values ◽  
Joint Infections ◽  
Group 3 ◽  
Group 2 ◽  
Sensitivity Specificity ◽  
Group 1

<p class="abstract"><strong>Background:</strong> Acute bone infections like septic arthritis and osteomyelitis are a serious threat in management and diagnosis in the department of orthopaedics. Biochemical marker is needed with good sensitivity and specificity in diagnosing acute bone and joint infections. The aim of the present study was to study the role of PCT in conditions of septic arthritis and osteomyelitis.</p><p class="abstract"><strong>Methods:</strong> A two year prospective study was done and cases were grouped into three group and laboratory parameters TC, ESR, CRP and PCT were measured. The sensitivity, specificity and predictive values were compared using SPSS software version 20.<strong></strong></p><p class="abstract"><strong>Results:</strong> 238 patients, (males- 154 &amp; Females– 84) with mean age 34.1±8.20 years. Group-1 included 52 patients with raised PCT and MRSA and <em>Klebsiella</em> as the common isolates. Group-2 with 89 patients and mean PCT in the study group was 4.99 ng/ml. Ninety seven were included in Group-3. The mean PCT value was 2.6 ng/ml. In group-1, the specificity of PCT (comparing Group-1 &amp; 3) was 96.8 [95% CI, 94.2 -98.4], the sensitivity (26% [3.2-60.1], the PPV 16.1% [95% CI 2.3-48.3] and the NPV was 98% [95% CI, 95.5-99.8].</p><p class="abstract"><strong>Conclusions:</strong> To conclude our study, highlights the role of PCT as a sensitive and specific marker in diagnosing cases of septic arthritis and Osteomyelitis. This opens a gateway to further research in evaluating the PCT effectiveness as a response marker to treatment. PCT is more sensitive than CRP in acute bone and joint bacterial infections and raises early and faster.</p>

Effects of Diluent Volume of a Single Dose of Epidural Bupivacaine in Parturients During the First Stage of Labor

1998 ◽  
Vol 23 (2) ◽  
pp. 134-141 ◽  
Author(s):  
Frank Christiaens ◽  
Christian Verborgh ◽  
Ann Dierick ◽  
Frédéric Camu
Keyword(s):  
Single Dose ◽  
Pain Relief ◽  
Opioid Analgesics ◽  
Pain Scale ◽  
Labor Pain ◽  
Similar Degree ◽  
Epidural Bupivacaine ◽  
Group 3 ◽  
Group 2 ◽  
Group 1

Background and Objectives0.1% bupivacaine for obstetric epidural analgesia is given by infusion, using a loading dose of a higher concentration alone or in combination with opioid analgesics. A single dose of 0.1% without any additive for relief of first-stage labor pain has not yet been documented.MethodsFifty-eight primiparae in active labor and with less than 5 cm cervical dilatation received 20 mg epidural bupivacaine diluted in 4 mL [group 1: 0.5% (I)], 10 mL [group 2: 0.2% (II)], or 20 mL [group 3: 0.1% (III)]. Pain relief, dermatomal spread, and motor block were assessed.ResultsVisual analog pain scale (VAS) was significantly lower in group 2 (0.88 ± 1.34) and group 3 (0.25 ± 0.61) than in group 1 (4.37 ± 2.57). Onset and time to maximum analgesia was significantly shorter in group 2 than in group 3. Mean duration of analgesia was 120 ± 21 minutes in group 3, 100 ± 26 in group 2, and 43 ± 21 in group 1. The mean numbers and upper limits of dermatomes blocked did not differ between groups 2 and 3, but were higher than in group 1. Motor blocks in groups 2 and 3 were more extensive than in group 1 with no difference between groups 2 and 3. Ten mL 0.2% or 20 mL 0.1% epidural bupivacaine results in a similar degree of pain relief, superior to that following 4 mL 0.5%, while duration was longest after 20 mL 0.1%.ConclusionsAnalgesia lasts significantly longer following 20 mL 0.1% bupivacaine than following 10 mL 0.2% bupivacaine when given for first-stage labor pain. Four milliliters 0.5% bupivacaine results in inadequate pain relief.

The Penetration of Ofloxacin into Human Aqueous Humor Given by Various Routes

1998 ◽  
Vol 8 (1) ◽  
pp. 33-36 ◽  
Author(s):  
S. Hanioglu-Kargi ◽  
N. Basci ◽  
H. Soysal ◽  
A. Bozkurt ◽  
E. Gürsel ◽  
...  
Keyword(s):  
Aqueous Humor ◽  
Bacterial Infections ◽  
High Performance ◽  
Cataract Extraction ◽  
The Other ◽  
Group 4 ◽  
Significant Difference ◽  
Group 3 ◽  
Group 2 ◽  
Group 1

This study was designed to measure the concentration of ofloxacin in aqueous humor after topical, oral and intravenous administration in 50 patients undergoing cataract extraction. In Group 1, ofloxacin 0.3% eyedrops were topically instilled ten times and the aqueous humor concentration was 2.73 ± 0.88 μg/ml. In Group 2, ofloxacin 0.3% eyedrops were topically instilled six times and the aqueous humor concentration was 0.84 ± 0.61 μg/ml. Aqueous humor concentration 12 hours after 200 mg oral dose in Group 3, was 0.38 ± 0.12 μg/ml. In Group 4, patients were given ofloxacin as a single intravenous 200 mg dose and the aqueous humor concentration 2 hours after the end of infusion was 0.45 ± 0.11 μg/ml. Concentrations were determined by high performance liquid chromatography (HPLC) with fluorescence detection. There was a significant difference between Group 1 and the other groups, but not between Group 2 and Groups 3, 4. It was concluded that ofloxacin penetrates the corneal and the blood-aqueous barriers and can achieve good aqueous levels when given topically and systematically. Ofloxacin can be applied topically for external bacterial infections such as conjunctivitis and keratitis. Systematically administered ofloxacin reached higher levels than the MIC for some bacteria which cause endophthalmitis.

The dynamics of the host-parasite relationship

Parasitology ◽  
1964 ◽  
Vol 54 (3) ◽  
pp. 527-544 ◽  
Author(s):  
A. D. Donald ◽  
J. K. Dineen ◽  
J. H. Turner ◽  
B. M. Wagland
Keyword(s):  
Single Dose ◽  
Egg Production ◽  
Technical Assistance ◽  
Parasitic Infection ◽  
Treatment Groups ◽  
Infective Larvae ◽  
Total Fecundity ◽  
Group 3 ◽  
Group 2 ◽  
Group 1

The studies presented in this paper describe the effects of control exerted by the immunological response of the host (sheep) on the developmental stages and fecundity of the parasite Nematodirus spathiger. Thirty Merino lambs, maintained worm-free, were randomly divided among three treatment groups each containing ten animals. The group 1 lambs were each given a single dose of 50,000 infective larvae, the group 2 animals were given a single dose of 130,000 infective larvae, and the group 3 animals were given twenty-five consecutive daily doses of 2000 infective larvae. Group fecundity was estimated by performing worm egg counts on daily faecal samples and development of the parasite burden was followed by carrying out differential worm counts on animals slaughtered at crucial stages during the infections. Total fecundity was greatest in group 1 and least in group 3 with group 2 intermediate. An inverse relationship between total fecundity and percentage retardation of development (percentage of 4th-stage larvae in the total worm burden) was demonstrated between the three treatment groups.The results of the studies also show that control of the parasitic infection is mediated about threshold levels of immunological responsiveness and is expressed by (1) elimination at the infective (L3) stage, (2) retardation of development at the L4 stage, (3) reduction in egg production of the adult female, (4) elimination of adult worms, and (5) discrimination against the female in both the degree of retardation in the L4 stage and the extent of elimination in the adult stage.Great variation in response was observed between individuals within treatment groups. The source of variation is attributed to differences in degree of antigenic disparity of the parasite with individual members of the heterozygous host population in which antigenic characters are not uniformly segregated.The concept of ‘fitness’ of the parasitic species was introduced into the discussion to provide a rational interpretation of the results.We are indebted to Dr S. S. Y. Young, Division of Animal Genetics, C.S.I.R.O., for advice and assistance with the statistical analyses, which were performed by Mrs M. Tonkin, and to Dr D. F. Stewart for his constructive criticism of the manuscript. Careful technical assistance was given by Mr E. Teleki and Misses Helen Giller and Berenice Merchant.

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