Effect Of Passive Immunization Research Articles

The effect of passive immunization on the acute phase of infection in a murine model of EHV‐1.

Equine herpes virus 1 causes respiratory infection in equine world-wide. Virus replicates in the respiratory tissues in ciliated and non-ciliated epithelial cells lining the nasal turbinate bones, trachea, bronchi, bronchioles, and type I and type II pneumocytes, and becomes viraemic causing myeloencephalopathy (paresis) and retinopathy. The virus later becomes latent. While active the virus crosses the placenta and leads to abortion of dead or dying foetuses and neonatal death. Infected horses show transient immunity after natural or experimental infection and immune responses to EHV-1 begin to decline after a few months of infection. Due to the transient nature of the immune response, horses are prone to subsequent reinfection and as a result development of an effective vaccine continues to be a challenge till to date. In order to discover the role of neutralizing antibodies in the pathogenesis of EHV-1 infection, we studied the role of neutralizing antibodies in a murine model of infection during the acute stage of infection by passively immunizing mice by the subcutaneous route with a pre-immune or hyperimmune polyclonal rabbit neutralizing serum 24 hours before virus infection. Mice were challenged intranasally with live EHV-1 virus and virus replication in the respiratory tissues was studied on day 3 and 5 post infection (p.i., acute stage of infection). The effect of passive immunization was also studied on viraemia by infectious centers assays from buffy coat cells. Slight reduction in virus titres in the respiratory tissues and level of viraemia was noted on day 3 p.i, but this difference was not significant. However significant reduction was seen in virus titres both in respiratory tissues and on the state of viraemia on day 5 in passively immunized animals compared with the controls given pre-immune sera from the same rabbit. The sera of passively transferred mice were also tested for presence of rabbit neutralizing antibodies on day 3 and 5 (days 4 and 6) of antibody transfer, suggesting that for complete protection neutralizing IgA may be required at the mucosal surface to stop or otherwise inhibit the viral attachment and thereby explain the differences in viral titres. These results of antibody transfer at an acute stage of infection will be discussed in this communication.

Measurement of transfer of colostral passive immunity in dairy calves

Measurement of transfer of colostral passive immunity in dairy calves

Effects of Passive Immunization by Anti-Gingipain IgY on the Oral Health of Cats Fed Kibble Diets

Porphyromonas gulae is one of the key microorganisms in biofilm dysbiosis that leads to periodontal disease, a prevalent disease in cats. Gingipains are proteases secreted that promote the disruption of cell adhesion and the differentiation of osteoclasts. The use of anti-gingipain immunoglobulin Y (IgY-GP) has emerged as a promising alternative to conventional prevention and treatment methods. The aim of this study was to evaluate the efficacy of IgY-GP on different parameters related to oral health in cats. Twenty adult mixed-breed cats were divided into 2 groups of 10 cats fed with 2 extruded diets differing only by coating. The control group received a coating of 4 g/kg of powdered egg and the test group received a coating of 4 g/kg of IgY-GP. The experiment followed a crossover design with 2 periods, each lasting 40 days with a washout period of 30 days. The evaluated parameters were plaque, calculus, gingivitis index, and percentage of Porphyromonas gingivalis of the oral cavity (%PG-OC) at baseline and after 40 days of diet consumption. All cats remained healthy throughout the study and no adverse reactions or side effects were observed. After 40 days of IgY-GP consumption, the plaque index was significantly lower compared to the baseline ( P = .0133). There were no significant changes in calculus index, gingivitis index, and %PG-OC between groups after 40 days ( P > .05). The consumption of IgY-GP reduces plaque accumulation, which may lead to an improvement in the oral health of adult cats.

Anti-\u03b1-synuclein immunotherapy reduces \u03b1-synuclein propagation in the axon and degeneration in a combined viral vector and transgenic model of synucleinopathy

Neurodegenerative disorders such as Parkinson’s Disease (PD), PD dementia (PDD) and Dementia with Lewy bodies (DLB) are characterized by progressive accumulation of α-synuclein (α-syn) in neurons. Recent studies have proposed that neuron-to-neuron propagation of α-syn plays a role in the pathogenesis of these disorders. We have previously shown that antibodies against the C-terminus of α-syn reduce the intra-neuronal accumulation of α-syn and related deficits in transgenic models of synucleinopathy, probably by abrogating the axonal transport and accumulation of α-syn in in vivo models. Here, we assessed the effect of passive immunization against α-syn in a new mouse model of axonal transport and accumulation of α-syn. For these purpose, non-transgenic, α-syn knock-out and mThy1-α-syn tg (line 61) mice received unilateral intra-cerebral injections with a lentiviral (LV)-α-syn vector construct followed by systemic administration of the monoclonal antibody 1H7 (recognizes amino acids 91-99) or control IgG for 3 months. Cerebral α-syn accumulation and axonopathy was assessed by immunohistochemistry and effects on behavior were assessed by Morris water maze. Unilateral LV-α-syn injection resulted in axonal propagation of α-syn in the contra-lateral site with subsequent behavioral deficits and axonal degeneration. Passive immunization with 1H7 antibody reduced the axonal accumulation of α-syn in the contra-lateral side and ameliorated the behavioral deficits. Together this study supports the notion that immunotherapy might improve the deficits in models of synucleinopathy by reducing the axonal propagation and accumulation of α-syn. This represents a potential new mode of action through which α-syn immunization might work.

Effects of Passive Immunization against Peptide Tyrosine Tyrosine on the Activity of Digestive Enzymes in Rats

The object of this study was to investigate the effect of serum antibody of peptide tyrosine tyrosine on activities of digestive enzymes in rats. A total of sixty sprague-dawley (SD) rats weighing 87.77 ± 1.61 g were randomly allocated to 1 of 4 dose treatment:0 (control), 50 μL, 100 μL, or 200 μL peptide tyrosine tyrosine antiserum during the 21-d experimental period. The activity of amylases and lipases in the pancreas and duodenum as well as gastric pepsin was measured at the end of the study. The results showed that the activity of lipases in the pancreas and duodenum increased with increasing peptide tyrosine tyrosine antiserum level, but obvious tendency of pancreatic lipases activity between all treatments was not observed(P>0.05). The lipase activity in the duodenum showed a significant increase (P 0.05) among groups, but the group treated with 200 μL of PYY antiserum showed the highest activity. In conclusion, the injection of peptide tyrosine tyrosine antiserum improved nutrition utilization rate and activity of digestive enzymes in a dose dependent manner in rats.

Effect of passive immunization on immunogenicity and protective efficacy of vaccination against a Mexican low-pathogenic avian H5N2 influenza virus

Despite the use of vaccines, low-pathogenic (LP) H5N2 influenza viruses have continued to circulate and evolve in chickens in Mexico since 1993, giving rise to multiple genetic variants. Antigenic drift is partially responsible for the failure to control H5N2 influenza by vaccination; the contribution of maternal antibodies to this problem has received less attention. We investigated the effect of different antisera on the efficacy of vaccination and whether booster doses of vaccine can impact immune suppression. While single doses of inactivated oil emulsion vaccine to currently circulating H5N2 influenza viruses provide partial protection from homologous challenge, chickens that receive high-titer homologous antisera intraperitoneally before vaccination showed effects ranging from added protection to immunosuppression. Post-infection antisera were less immunosuppressive than antisera obtained from field-vaccinated chickens. Homologous, post-infection chicken antisera provided initial protection from virus challenge, but reduced the induction of detectable antibody responses. Homologous antisera from field-vaccinated chickens were markedly immunosuppressive, annulling the efficacy of the vaccine and leaving the chickens as susceptible to infection as non-vaccinated birds. Booster doses of vaccine reduced the immunosuppressive effects of the administered sera. Vaccine efficacy against LP H5N2 in Mexico can be severely reduced by maternal antibodies. Source-dependent antisera effects offer the possibility of further elucidation of the immunosuppressive components involved.

Effects of Passive Immunization against Peptide Tyrosine Tyrosine on the Growth Performance and Endocrine Hormone Levels in Blood Serum of Rats

The aim of this study was to determine the effects of immunization against Peptide tyrosine tyrosine (PYY) on the growth performance and endocrine hormone levels in the blood serum of rats. Sixty Sprague-Dawley rats were randomly assigned to four treatment groups, with five replicates in each group and three rats for each replicate. The antiserum of PYY was injected into the rats thrice every 8 days at the concentrations of 0 (control), 50, 100 and 200 &muL. Throughout the experimental period, the rats were given free access to food pellets and water. The growth performance of the animals, including their average daily gain, average daily feed intake and feed/gain ratio, was recorded. The blood samples of PYY, Neuropeptide Y (NPY), leptin, gastrin and insulin concentrations were measured. The good effects of PYY antiserum on the growth performance and serum indexes of treat groups were observed in this trial, especially in group 3 rats. The average daily gain recorded for days 8-14 and 15-21 in group 3 increased by 7.23% (p<0.05) and 9.79% (p<0.05) respectively, compared with the control group. The feed intake in group 3 was also higher than that in the control group by 19.73% (p<0.05), 14.47% (p<0.05) and 12.09% (p<0.05) on days 0-7, 814 and 1521, respectively. However, no significant difference in feed/gain ratio between the treatment and control groups was detected. Moreover, the NPY, leptin, insulin and gastrin concentrations in group 3 significantly increased by 34% (p<0.05), 251% (p<0.01), 589% (p<0.01) and 31.93% (p<0.01) respectively, compared with the control group, whereas the level of PYY significantly decreased by 57.82% (p<0.01). In conclusion, the growth, ingestion and some metabolism-related hormones with good effects on the regulation of feed intake and energy metabolism can be improved by passive immunization against PYY rather than by causing immunological stress in animals.

Effect of passive immunization against leptin on ovarian follicular development in prepubertal mice

Leptin has been demonstrated to be essential for reproduction. However, all the relevant studies reported to date have investigated either the effect of a complete absence of leptin both centrally and peripherally, or excess leptin administration. The aim of this present study was to investigate the effect of reducing peripheral leptin concentrations on ovarian follicular development in prepubertal animals via administration of an anti-leptin antibody. Pre-pubertal female mice were administered anti-leptin antibody under the skin behind the head for four days, with or without gonadotropins, and ovaries were weighed and collected for follicle counting. Control animals were treated with non-immune serum. Passive immunization against leptin, with or without gonadotropins, resulted in a significant increase in ovarian weight compared with control ovaries. Furthermore, the ovaries from the anti-leptin group had significantly greater numbers of primary follicles per ovarian section than the control group, thus suggesting an increase in the transition of primordial to primary follicles after treatment. Interestingly, animals treated with anti-leptin plus gonadotropins had a significantly higher number of Graafian follicles in their ovaries compared with the other groups. Collectively, the results of the present study indicate that reduction of leptin in the circulation promotes ovarian follicle development in female mice, suggesting that peripheral leptin acts as an inhibitor of ovarian follicle development.

Effect of passive immunization by anti-gingipain IgY on periodontal health of dogs

Anti-gingipain IgY (IgY-GP), known as hyperimmune γ-livetin from egg yolk, inhibits the enzyme activity, growth and adherence of &lt;em&gt;Porphyromonas gingivalis&lt;/em&gt; to gingival epithelial cells. Our objective was to evaluate the efficacy of IgY-GP on periodontal health of dogs. IgY-GP was prepared from the egg yolk of hens immunized with the gingipain from &lt;em&gt;Porphyromonas gingivalis&lt;/em&gt; ATCC 33277. Two &lt;em&gt;in vivo&lt;/em&gt; trial models were conducted on 15 adult dogs with periodontitis by giving IgY-GP-supplemented dog feed for 8 weeks and direct application of the IgY in dental ointment to the periodontal pockets at weekly interval for 4 weeks. Clinical parameters including gingivitis, periodontitis, oral health index, bleeding on probe (BOP), pocket depth (PD), and dental calculus removal pattern for selected premolar teeth were recorded at baseline, 4 and 8 weeks post treatment.IgY-GP showed strong cross-reactivity with gingipain from &lt;em&gt;Porphyromonas gulae&lt;/em&gt; and inhibited the enzyme activity &lt;em&gt;in vitro&lt;/em&gt;. In the dog trials, IgY-GP resulted in significant improvement of oral health parameters including gingivitis and periodontitis scores, BOP, dental calculus removal. No adverse events during and after antibody applications were noted. Oral immunotherapy by using IgY-GP is a new promising alternative to conventional preventive and therapeutic methods to improve oral health status in dogs.

Effect of passive immunization by anti-gingipain IgY on periodontal health of dogs

Effect of passive immunization by anti-gingipain IgY on periodontal health of dogs

P4‐408: Therapeutic effect of passive immunisation with a monoclonal antibody against low molecular weight pyroglutamate oligomers in a preclinical Alzheimer mouse model

P4‐408: Therapeutic effect of passive immunisation with a monoclonal antibody against low molecular weight pyroglutamate oligomers in a preclinical Alzheimer mouse model

Maternal vaccination against nicotine reduces nicotine distribution to fetal brain in rats.

Cigarette smoking during pregnancy is associated with a variety of adverse fetal outcomes. Nicotine is a likely contributor to these adverse effects, with fetal brain as one target organ. Vaccination of adult male rats against nicotine has been shown to reduce nicotine distribution to the brain. The current study examined whether vaccination of female rats before pregnancy would reduce the distribution to fetal brain of a single nicotine dose administered during gestation. Female rats immunized with a nicotine conjugate vaccine received a single dose of nicotine 0.03 mg/kg i.v. on gestational day 16 to 22. Five minutes later, vaccinated rats had substantially higher bound and lower unbound serum nicotine concentration and lower brain nicotine concentration than controls. Fetal brain nicotine concentration was reduced by 43% in vaccinated rats, comparable to the reduction in the maternal brain nicotine concentration. The whole-fetus nicotine concentration was not altered by vaccination. A similar experiment was performed in which pregnant rats were passively immunized with rabbit nicotine-specific IgG 7 or 21 mg/kg just before nicotine dosing. The effects of passive immunization on nicotine distribution in the mother were IgG dose-related and the higher dose reduced nicotine distribution to fetal brain by 60%. These data suggest that vaccine effects on nicotine distribution to serum and brain are similar in pregnant female rats to those previously reported in adult males. Vaccination of female rats before pregnancy, or passive immunization during pregnancy, can reduce the exposure of fetal brain to a single dose of maternally administered nicotine.

Effect of passive immunization with buffalo follicular fluid antisera on ovarian activity in guinea pigs.

Ovarian activity and follicular populations were studied in guinea pigs (Cavia porcellus) following administration of antisera against buffalo follicular fluid (buFF). Antibodies were raised in rabbits and the titre tested by immunodiffusion assay. Fourteen guinea pigs cycling normally were randomized into two groups. Animals in Group I (n = 8) were treated (i.p.) with 0.5 ml antisera and in Group II (control, n = 6) with the same volume of normal rabbit serum at 12 h intervals on the 10th and 11th day of their oestrous cycle. They were sacrificed 24 h after onset of estrus when ovulation points were counted and ovaries processed for microscopical examination. Treatment with buFF-antisera increased ovulation rate (3.6 vs. 2.0; p < 0.01) but had no significant effect on the total number of follicles. However, the treatment reduced the percentages of atretic follicles in all size classes. These results indicated that the administration of a buFF-antisera produced in the rabbits increased ovulation rate in guinea pigs by reducing the incidence of atresia.

Effect of passive immunization against inhibin on FSH secretion, folliculogenesis and ovulation rate during the follicular phase of the estrous cycle in mares

Physiological roles of inhibin in mares were investigated by means of passive immunization using an antiserum to inhibin that had been raised in a castrated goat. Eight mares were given an intravenous injection of either 100 mL (n=4) or 200 mL (n=4) of inhibin antiserum 4 d after a single intramuscular injection of PGF2alpha on Day 8 after ovulation, 4 control mares were treated with 100 mL castrated goat serum in the same manner. Jugular vein blood samples were collected after treatment with the serum until 192 h post treatment. Follicular growth and ovulations were monitored by ultrasound examination at 24-h intervals. The ability of the inhibin antiserum to neutralize the bioactivity of equine inhibin was examined in vitro using a rat pituitary cell culture system. Suppression of secretion of FSH from cultured rat pituitary cells by equine follicular fluid was reversed by the addition of increasing doses of the inhibin antiserum, thereby indicating its bioactivity. Plasma levels of FSH and estradiol-17β were higher in mares treated with the inhibin antiserum. The ovulation rate was significantly higher in mares treated with antiserum (100 mL =3.75 ± 0.63; 200 mL =4.50 ± 0.65) than in control mares (1.25 ± 0.25). These results demonstrate that inhibin is important in regulating FSH secretion and folliculogenesis in mares. They also show that neutralization of the bioactivity of inhibin may become a new method for the control of folliculogenesis and ovulation rate in mares.

Anticapsular polysaccharide antibodies and nasopharyngeal colonization with Streptococcus pneumoniae in infant rats.

To evaluate the effect of passive immunization with anticapsular antibodies on nasopharyngeal carriage, two models of Streptococcus pneumoniae colonization were developed in infant rats. In a direct inoculation model, 3- to 4-day-old infant rats were intranasally inoculated with 2 x 10(5) cfu of S. pneumoniae type 3 or 6 x 10(3) cfu of S. pneumoniae type 23F. In an intralitter transmission model, 2 infant rats were intranasally inoculated with 10(3) cfu of pneumococcus type 3 or type 19F and placed in a cage containing 10 infant rats. Pretreatment with bacterial polysaccharide immune globulin led to a significant reduction in colonization of contact animals with S. pneumoniae type 3 or 19F in the intralitter transmission model (P < .05). No effect of immune globulin could be demonstrated in the direct inoculation model. These results indicate that systemic anticapsular antibodies conferred significant protection against nasopharyngeal acquisition by intralitter spread of S. pneumoniae type 3 and 19F.

Effects of passive immunization using antibody against an α-inhibin peptide on follicle-stimulating hormone concentrations and litter size in sows

The objective of the experiment was to determine whether passive immunization against inhibin at weaning would increase FSH secretion and thereby influence postweaning reproductive performance in sows. Commercial Yorkshire sows (n = 173) were assigned within parity to 5 α-inhibin fragment antibody (α-IF-Ab) dosage groups: 0 (control), 3.25, 6.5, 13 and 26 RP-2 kU/kg α-IF-Ab. Antibody had been semipurified from ovine antisera raised against α-IF, a peptide that mimicked the N-terminal region of inhibin's α-subunit. A RP-2 U refers to a laboratory reference preparation. Sows were administered a single intramuscular injection of control solution or α-IF-Ab just before 21-d-old piglets were weaned. Blood samples were taken immediately before immunization and 24 h later. Sows were bred upon expression of estrus. Serum α-IF-Ab titers in sows 24 h following passive immunization increased (P < 0.001) with dosage. In control sows serum FSH concentrations decreased 24% by 24 h postweaning (P < 0.001). The decrease was diminished or prevented by α-IF-Ab treatment in a dose-responsive manner (P < 0.001). Most (167/173) sows were bred within 10 d postweaning, and wean-to-service intervals tended (P < 0.1 ) to be shorter in the 13 and 26 RP-2 kU/kg α-IF-Ab dosage groups. Farrowing rate was 72% (124/173) and was similar among sows in the α-IF-Ab dosage groups. Litter size, expressed as total or live piglets born per sow or per sow farrowed, was unchanged by α-IF-Ab treatment. Results demonstrate that 1) inhibin plays a key role in regulating FSH secretion at weaning, and 2) blocking the acute postweaning drop in FSH secretion has little if any effect on subsequent reproductive performance.

Effect of passive immunization or maternally transferred immunity on the antibody response to a genetic vaccine to rabies virus.

A plasmid vector, termed pSG5rab.gp, expressing the glycoprotein of rabies virus was tested in young adult or neonatal mice in the presence of maternally transferred immunity or passively administered antibodies to rabies virus for induction of an antibody response. Mice born to rabies virus-immune dams developed an impaired antibody response to genetic immunization at 6 weeks of age, as had been previously observed upon vaccination with an inactivated viral vaccine. Similarly, mice passively immunized with hyperimmune serum showed an inhibited B-cell response upon vaccination with the pSG5rab.gp vector, resulting in both cases in vaccine failures upon challenge with a virulent strain of rabies virus. In contrast, the immune responses of mice vaccinated as neonates in the presence of maternal immunity or upon passive immunization to rabies virus with the pSG5rab.gp construct were only marginally affected.

Effects of passive immunization against inhibin on ovulation rate and embryo recovery in holstein heifers

The effects of acute neutralization of endogenous inhibin on ovulation rate and circulating FSH levels were investigated. Nine or ten days after estrus, 5 heifers were given a single injection of 75 ml iv inhibin antiserum produced in a castrated male goat, while another 5 were given the same amount of a castrated male goat serum. All heifers were given injections of PGF2α im at 48 h and 60 h after the serum injection. Those exhibiting an estrus were artificially inseminated with frozen-thawed semen. Seven or eight days after the insemination, ova or embryos were collected using a non-surgical method. Administration of inhibin antiserum resulted in a significant increase in the number of medium-sized follicles compared with the number in the control animals. The number of large follicles in the inhibin-neutralized animals was 4.8 ± 2.4 (mean ± SEM; n = 5) on the day of estrus, while there was a single large follicles in the ovaries of control animals. Seven or eight days after estrus, 3 to 16 ova or embryos were recovered from 4 of 5 animals, and 64 % of the total ova/embryos were transferable. Administration of inhibin antiserum produced a significant increase in the concentrations of plasma FSH from 12 to 72 h after the serum injection compared with the levels in the control animals (P < 0.05). After the onset of estrus, preovulatory LH and FSH surges were noted in inhibin-neutralized animals and magnitude of the rise in each hormone was similar to the control animals. The present study demonstrates that a single injection of the inhibin antiserum induces multiple ovulations probably by enhancing FSH secretion, and that recovery of embryos is equal to that observation after an ordinary FSH treatment.

Pathogenic antibodies in women with obstetric features of antiphospholipid syndrome who have negative test results for lupus anticoagulant and anticardiolipin antibodies

OBJECTIVE: Our goal was to determine whether women with clinical features of antiphospholipid syndrome but negative test results for lupus anticoagulant and anticardiolipin antibodies have pathogenic antibodies not identified by currently used methods. STUDY DESIGN: Sera were obtained from women with clinical features associated with antiphospholipid antibodies who had negative test results for lupus anticoagulant and anticardiolipin antibodies (antiphospholipid syndrome–like). We studied (1) the effect of passive immunization with their purified immunoglobulin G fraction on murine pregnancy ( n = 35) and (2) the presence of antiphospholipid antibodies other than lupus anticoagulant or anticardiolipin antibodies ( n = 39). Sera were also retested for anticardiolipin antibodies and lupus anticoagulant. RESULTS: Fetal loss occurred in 235 of 1088 (22%) pups in 137 mice immunized with immunoglobulin G fraction from antiphospholipid syndrome–like women compared with 23 of 402 (6%) pups in 53 control mice. Immunoglobulin G from 11 study patients resulted in the loss of at least one third of the exposed pups. Five women had positive levels of antiphosphatidylserine antibodies (>99th percentile). All levels were low positive, and three women also had low-positive levels of anticardiolipin antibodies on repeat testing. Five of the 11 (45%) women whose immunoglobulin G fractions caused at least 33% fetal loss also had positive test results for antiphospholipid antibodies. CONCLUSIONS: A subset of women with clinical disorders suspicious for antiphospholipid syndrome but who had negative test results for lupus anticoagulant and anticardiolipin antibodies by current methods have serum immunoglobulin G that is pathogenic to murine pregnancy. Testing for pathogenic immunoglobulin G may provide additional means to identify women with an as yet uncharacterized immune condition. The clinical relevance of low levels of antiphospholipid antibodies in these women remains unproved. (Am J Obstet Gynecol 1997;176:628-33.)

Concentration of gonadotropin-releasing hormone receptor messenger ribonucleic acid in pituitary tissue of orchidectomized sheep: effect of passive immunization against gonadotropin-releasing hormone.

The effect of immunoneutralization of gonadotropin-releasing hormone (GnRH) on LH secretion and concentrations of GnRH receptor, GnRH receptor mRNA, and gonadotropin subunit mRNA in pituitary tissue of orchidectomized sheep (wethers) was assessed. Thirty-six wethers were assigned at random to one of six treatment groups (six wethers per group). Thirty wethers (groups 2 to 6) received 200 ml, (i.v.) of anti-GnRH antisera at passive immunization (PI). Anterior pituitary tissue was collected .5, 1, 2, 4, or 8 d after PI from wethers in groups 2 to 6, respectively. Pituitary tissue was also collected from unimmunized wethers (Group 1). Intravenous administration of anti-GnRH sera increased anti-GnRH activity to 69.1 +/- 7% (percentage of total 125I-labeled GnRH bound by a 1:1,000 serum:GEL-PBS dilution) within 1 h of PI. Anti-GnRH activity declined gradually during the period after PI, and 8 d after PI anti-GnRH activity was 57.2 +/- 1.7%. Serum concentration of LH was significantly reduced, relative to the pretreatment (16.1 +/- 1.8 ng/mL) level, within 4 h (7.6 +/- 1.5 ng/mL) of PI, and the LH level was 10% of the pretreatment concentration 8 d after PI (1.6 +/- 0.2 ng/mL). Steady-state concentration of GnRH receptor mRNA decreased progressively during the period after PI and was significantly reduced, relative to the level in unimmunized control wethers (.44 +/- .03 pg/micron total RNA) d after PI. Tissue concentrations of GnRH receptor and mRNA for the alpha, LH alpha, and FISH beta subunits were also reduced (P < .05) by PI. These data indicate that maintenance of steady-state concentrations of GnRH receptor and GnRH receptor mRNA requires continued GnRH stimulation.