Antibody response to viral antigens

The Cellular Chaperone Heat Shock Protein 90 Is Required for Foot-and-Mouth Disease Virus Capsid Precursor Processing and Assembly of Capsid Pentamers

Productive picornavirus infection requires the hijacking of host cell pathways to aid with the different stages of virus entry, synthesis of the viral polyprotein, and viral genome replication. Many picornaviruses, including foot-and-mouth disease virus (FMDV), assemble capsids via the multimerization of several copies of a single capsid precursor protein into a pentameric subunit which further encapsidates the RNA. Pentamer formation is preceded by co- and posttranslational modification of the capsid precursor (P1-2A) by viral and cellular enzymes and the subsequent rearrangement of P1-2A into a structure amenable to pentamer formation. We have developed a cell-free system to study FMDV pentamer assembly using recombinantly expressed FMDV capsid precursor and 3C protease. Using this assay, we have shown that two structurally different inhibitors of the cellular chaperone heat shock protein 90 (hsp90) impeded FMDV capsid precursor processing and subsequent pentamer formation. Treatment of FMDV permissive cells with the hsp90 inhibitor prior to infection reduced the endpoint titer by more than 10-fold while not affecting the activity of a subgenomic replicon, indicating that translation and replication of viral RNA were unaffected by the drug.IMPORTANCE FMDV of the Picornaviridae family is a pathogen of huge economic importance to the livestock industry due to its effect on the restriction of livestock movement and necessary control measures required following an outbreak. The study of FMDV capsid assembly, and picornavirus capsid assembly more generally, has tended to be focused upon the formation of capsids from pentameric intermediates or the immediate cotranslational modification of the capsid precursor protein. Here, we describe a system to analyze the early stages of FMDV pentameric capsid intermediate assembly and demonstrate a novel requirement for the cellular chaperone hsp90 in the formation of these pentameric intermediates. We show the added complexity involved for this process to occur, which could be the basis for a novel antiviral control mechanism for FMDV.

Identification of a conserved linear epitope on the VP1 protein of serotype O foot-and-mouth disease virus by neutralising monoclonal antibody 8E8

Foot-and-mouth disease virus (FMDV) serotype O remains an important threat to animal husbandry worldwide, and the variability of the virus presents a major problem for FMDV vaccine design. High-affinity neutralising antibodies against a conserved epitope could provide protective immunity against diverse subtypes of FMDV serotype O and protect against future pandemics. We generated a novel monoclonal antibody (MAb) 8E8 that potently neutralised infection of FMDV O/YS/CHA/05 both in vitro and in vivo. Screening of a phage-displayed random 12-peptide library revealed that MAb 8E8 bound to phages displaying a consensus motif GDLNVRT, which is highly homologous to (146)GDLQVLT(152) of the FMDV VP1 protein. Given that MAb 8E8 showed reactivity with the (146)GDLQVLT(152) motif, we proposed that this motif represented a linear B-cell epitope of the VP1 protein. Western blot analysis revealed that the epitope peptide could be recognised by the positive sera from serotype O FMDV-infected pigs. The (147)DLQVLT(152) motif was the minimal requirement for reactivity as demonstrated by reactivity of MAb 8E8 with several truncated peptides derived from the motif. For further mapping, a set of different extended motifs derived from the minimally reactive epitope was expressed with a GST-tag and subjected to western blot. The results showed that a 10-aa peptide (145)RGDLQVLTPK(154) was the minimal unit with maximal binding activity to MAb 8E8. Subsequent alanine scanning mutagenesis studies revealed that D(147), Q(149) and V(150) are crucial for MAb 8E8 binding. Furthermore, the epitope was found to be highly conserved among different topotypes of serotype O FMDV through sequence alignment analysis and detection of MAb 8E8 for affinity to some isolates collected in China. Thus, the 8E8 epitope identified here should be helpful for designing epitope-based, intra-typic, cross-protective vaccines of serotype O FMDV.

Natural and vaccine induced immunity to FMD

A brief overview of the foot-and-mouth disease (FMD) literature over the last 100 years will give the impression that a great deal is known about the immune response of livestock to infection and vaccination. At the practical level, this is indeed the case and our knowledge is more than adequate in relation to the production and supply of potent vaccines for the control of the disease. The deficiencies in our understanding of the immune response are at the fundamental level and, arguably, stand in the way of its rational manipulation to achieve goals such as life-long immunity conferred by vaccination. Most of the research activity to date has focused on T cell dependency of the immune response of livestock and important B (and probably T) cell epitopes and has been used by researchers to design highly sophisticated novel vaccines and delivery systems. None of these, to the author's knowledge, exceeds the potency obtained with a good commercial vaccine. Although it is not yet possible to see a clear direction for the development of improved formulations, it is important to reflect on our current knowledge of natural and vaccine-induced immunity and some of the issues surrounding modern inactivated FMD vaccines. This process will perhaps help to discriminate the fact from the fiction and serve to focus on precisely what is needed or desirable for improved products.

Conceptual foundations for infectious disease surveillance

The purpose of this report is to offer concepts for consideration in developing infectious disease surveillance systems, defined here as active, formal, and systematic processes intentionally directed to rapidly seek out and identify infectious disease agents or disease. Performance of surveillance systems can be judged by their accuracy (sensitivity and specificity), precision (repeatability), timeliness, multiple utility, and value. Surveillance system operation and function necessary to achieve high performance are defined in part by characteristics of the specific infectious disease, including disease transition state dynamics, that define probabilities of being in the latent, infectious, or clinical phase of disease. Two key components of surveillance are the sampling scheme, which is intended to maximize the probability of capturing an infected animal or specimen as soon as possible after the herd has been exposed, and the diagnostic assays, which should maximize the probability of detecting the agent, or evidence of the agent, if it is present in the specimen, while minimizing the likelihood of a false-positive result. Proportional risk sampling, targeted sampling, and repeated sampling are strategies that can improve overall surveillance system accuracy and particularly the temporal sensitivity related to early detection. Hierarchical sampling schemes and multiplexed assays can maximize efficiency and improve utility by serving multiple surveillance systems and purposes. Development of the surveillance systems needed to address emerging and foreign animal diseases will necessarily require design and architecture that are highly probability-driven to maximize surveillance sensitivity and specificity and to minimize cost.

Longevity of antibody and cytokine responses following vaccination with high potency emergency FMD vaccines

The ability of high potency emergency foot-and-mouth disease (FMD) vaccines to promote sustainable immune responses in sheep and pigs following a single application was examined. All vaccine formulations induced a rapid seroconversion in both species, as expected, which was maintained at near peak titres for up to 6 months in sheep and 7 months in pigs. The Montanide ISA 206 formulation gave the best results in sheep. Vaccinated pigs challenged with homologous FMDV were protected from disease at 7 months post vaccination. Systemic levels of cytokines IL-6, IL-8, and in some pigs IL-12, increased following vaccination and were often maintained at an increased level for the duration of the trials. These initial results suggest that high potency vaccines may promote longer lasting immunity than the conventional lower potency vaccines in ruminants and a comparable response in pigs. Results indicate that in an outbreak situation, should emergency vaccination be done with these high potency vaccines, protection should be conferred for a long enough period for the outbreak to be brought under control without the need to revaccinate. Given the increased interval for re-vaccination the use of high potency vaccines for routine prophylactic campaigns could provide a more cost-effective and efficient means of maintaining herd immunity and is an area thus worthy of further examination.

Method for determining the equilibrium constant and the concentration of influenza virus IgG antihaemagglutinin antibody molecules by use of EIA titres determined with and without guanidine hydrochloride

A novel technique for determining the concentration of influenza virus antihaemagglutinin antibody molecules (A) of the IgG class and their equilibrium constant (K) is described which is based on recording EIA (enzyme-linked immunosorbent assay) guanidine titre ratios R (EIA titre determined in the absence of guanidine divided by EIA titre determined in the presence of 0.25 M guanidine hydrochloride). K is determined by using a regression line relating values of K to values of R. The line was established by testing antisera comparatively for K by means of equilibrium filtration and for R by EIA. The assay of A is based on the finding that the concentration of antibody molecules adsorbed at serum dilutions yielding an O.D. reading of 0.9 in the EIA test is within the experimental limits constant. Since K is known, this point of reference can be used to calculate A. For a panel of 57 influenza antisera, the A and K values determined by equilibrium filtration agreed well with the respective values determined by use of the novel technique.

Clearance of lymphocytic choriomeningitis virus in antibody- and B-cell-deprived mice

The role of antibody in immune recovery from infection with lymphocytic choriomeningitis virus (LCMV) strain WE was evaluated in B-cell-depleted mice. Mice were treated from birth with either affinity-purified rabbit anti-mouse immunoglobulin M (IgM), normal rabbit immunoglobulin, or, alternatively, an affinity-purified monoclonal rat anti-mouse IgM antibody (LO-MM-9); untreated mice served as controls. B-cell depletion was considered complete in specifically treated mice according to the following criteria: absence of a significant response to the B-cell mitogen lipopolysaccharide, absence of B cells expressing immunoglobulin on their surfaces, absence of detectable IgM or IgG in serum, and presence in the serum of free anti-IgM antibodies. In organs of mu-suppressed BALB/c mice, LCMV-WE replicated, dependent upon organ, at the same rate or more rapidly and, in general, to higher titers than in normal rabbit immunoglobulin-treated mice; untreated mice eliminated the virus most rapidly and showed lower virus titers. In addition, LCMV-primed control mice cleared a second LCMV challenge very rapidly and contained no virus by day 3, whereas mu-suppressed mice had virus in their blood and organs (except the spleen) up to days 3 to 6. The observed effects of anti-mu treatment may reflect the action of neutralizing antibodies (which so far have been difficult to demonstrate in vivo) or other antibody-dependent antiviral mechanisms which, together with T cells, efficiently control LCMV clearance.

Oncogenic viruses of domestic animals

The objective of this article is to review the relevant oncogenic viruses of small animals. Basic scientific principles that have been discovered by research into feline leukemia and other animal cancer viruses have enhanced our understanding of oncogenesis and have led to practical methods of cancer control and prophylaxis.

Detection of foot-and-mouth disease virus antibody using counterimmunoelectrophoresis and serum neutralisation tests

A comparative investigation was made on the applicability, sensitivity and specificity of counterimmunoelectrophoresis (CIEP) for the rapid detection of antibody to foot-and-mouth disease virus in cattle sera using as reference a standard serum neutralisation test. The CIEP test was sensitive and exhibited a reasonable specificity.

The effect of antiserum quality on strain specificity assessment of foot and mouth disease virus by the neutralization reaction

The factors affecting the virus strain specificity of antibody to foot an mouth disease virus prepared by a variety of protocols in several species were evaluated by neutralization tests. The time at which the serum was taken, the antigen dose given, whether or not revaccination had occurred and the animal species in which the sera were prepared, did not appear to affect the strain specificity of serum prepared to inactivated antigens when measured in neutralization tests, probably because of the restricted nature of the antigenic site involved. However, variation was observed with convalescent animal sera or sera from animals which had received trypsin cleaved virus were used. For these reasons banks of reference antisera are prepared as pooled sera using one or two inoculations of inactivated antigen.

Antigenic variation in foot-and-mouth disease: studies based on the virus neutralization reaction

The neutralization reaction is the most appropriate in vitro reference test system for assessing intratypic antigenic variation as it involves the antigenic determinants responsible for virus strain specificity and evoking protective antibody. Antigenic relationships determined in different neutralization test systems were independent of the system used and were assumed to truly reflect antigenic variation. The two-dimensional microneutralization test was found to be appropriate for foot and mouth disease (FMD) virus strain differentiation. To minimize test to test variation, comparisons are performed as matched pairs. The pooled variance of the test system is used to assess the significance of the relationships obtained. Antisera from convalescent animals were less specific than those from vaccinates. Serum quality seemed less critical for the virus neutralization than the complement fixation reaction. A system for FMD virus strain differentiation based on the use of the virus neutralization reaction taking into account the statistical and biological significance of observed r values is recommended.

Neutralization of sendai virus by the IgG subclass antibodies of the guinea pig

A comparative study was made of the neutralizing activities of IgG subclasses IgG1 and IgG2, fractionated from guinea pig antisera against Sendai virus. The yields of IgG2 from the antisera were about 16 times as much as those of IgG1. The neutralizing activity of IgG2 per unit weight was four times as high as that of IgG1. This neutralizing activity of both IgG subclasses was enhanced about 10 times by addition of antibodies to the L-chain of guinea pig immunoglobulin. It is suggested that, in the complement-dependent neutralization of the virus, IgG1 and IgG2 activate the complement through the alternative and the classical pathway, respectively.

Guanidine and heat sensitivity of foot-and-mouth disease virus (FMDV) strains

A study of the ability of 49 strains of FMD virus to replicate in BHK-21 monolayer cells maintained under a standard agar overlay containing 5.2 mM guanidine hydrochloride and to withstand heat inactivation at 54 degrees C for 1 h showed that strains belonging to serotypes C, O and Asia 1 were generally more resistant to guanidine and heat stable than the SAT 1, 2 and 3 serotypes. The type A viruses as a whole occupied an intermediate position between these two groups. In vitro passage in BHK-21 cells influenced the guanidine sensitivity of 3(O, C and SAT 3) of the 7 FMD serotypes suggesting that this is not a stable genetic marker. Heat stability of the FMD viruses, however, did not change on passage, suggesting that this is a stable characteristic inherent in any homogeneous FMD virus population.

Le diagnostic rapide des infections à virus respiratoire syncytial (RS) par le titrage des IgM sériques (immunofluorescence indirecte)

En janvier 1981, au cours d'une épidémie d'infections respiratoires survenue chez des enfants âgés de 1 à 3 mois, 9 sujets atteints de bronchiolites sévères ont été hospitalisés dans un service de pédiatrie et 11 cas sont survenus dans le service.

Pour le diagnostic rapide direct, les prélèments pharyngés et/ou des aspirations nasales effectués chez 10/11 malades étaient tardifs par rapport à l'apparition des symptômes. Le diagnostic direct n'a été positif que dans 2 cas, et l'isolement d'un virus a toujours été négatif.

Pour le diagnostic sérologique, dans 9 cas/16, le premier sérum a été prélevé après 5 jours d'évolution. La réaction d'immunofluorescence (IF) a permis de faire le diagnostic d'une infection à virus respiratoire syncytial dans 13 cas. La r'eaction de fixation du complément (FC) est restée négative dans tous les cas.

Pendant la période de novembre 1980 à janvier 1981, on a prélevé les sérums de 32 enfants et 13 adultes hospitalisés pour des infections respiratoires aiguës (bronchites et bronchopneumophathies) et les sérums de 35 adultes hospitalisés dans un service de transplantation rénale. La réaction d'IF indirecte n'a pas été plus sensible que la FC, mais elle a permis:o1)

de différencier les infections primaires des réinfections;

2)

de prouver que dans la majorité de ces réinfections (13 cas/17), on pouvait détecter des IgM;

3)

de porter un diagnostic de certitude rapide sur un seul sérum dans environ 60% des cas, alors que la FC était négative (1 cas) ou ne permettait qu'un diagnostic présomptif (10 cas).

Stability and immunogenicity of empty particles of foot-and-mouth disease virus

Three strains of foot-and-mouth disease virus were shown to contain significant amounts of naturally occurring 75S, empty particles as well as the infectious, 140S full particles. One of these strains--A Pando (1970)--was studied in detail. The empty particles from this virus strain were shown to have an observed sedimentation coefficient of 67S in 0.04 M phosphate buffer; they were labile in SDS, non-infectious and probably RNA-free and, on heating, they broke down to 12S subunits as did the 140S particles. The empty particles differed from the full particles in their polypeptide composition since they contained VP0, but there was no evidence for a diminished content of VP4. The 75S particles were shown to be present in significant amounts and to be stable to AEI inactivation. At 4 degrees C they were stable for at least two years. In guinea pigs they were as immunogenic as the 140S particles. The antisera raised against the 75S particles had the same serological specificity in neutralization tests as sera prepared against the 140S particle. It was concluded that the 75S particles from the A Pando (1970) strain of FMD virus may provide as important a contribution as 140S particles to the immunogenicity of inactivated vaccines prepared from this virus strain.

Rotavirus infections in families. A clinical and virological study

Among 25 family members of 8 children with acute rotavirus gastroenteritis (8 siblings and 17 adults) gastroenteritis was recorded in 9 (5 siblings and 4 adults), and minor symptoms in 8 (2 siblings and 6 adults). A rotavirus infection was diagnosed in 7 of the family members with gastroenteritis and was probably the cause of the disease in the remaining 2 in this group. Four of the 8 family members with minor symptoms were infected with rotavirus, whereas no infection was detected among the 8 family members without symptoms. Serological findings sugggested that infants and young children underwent a primary infection with rotavirus, whereas older children and adults probably were reinfected. Adults as well as children with rotavirus infection excreted virus and may have served as sources of infection.

Microneutralization tests for serological typing and subtyping of foot-and-mouth disease virus strains

A microneutralization test for serotyping of FMD viruses is described. It is based on earlier observations by Booth, Rweyemamu & Pay (1978) that dose-response relationships in quantal microneutralizations often deviated from linearity. The typing test described therefore utilizes undiluted virus preparations. In about 90% of samples a positive typing was obtained in contrast with about 50% for the complement fixation test. The test was also found to be susceptible to minimal quantities of heterotypic viral contamination. For strain differentiation the microneutralization test was carried out as a checkerboard test. When compared with the complement fixation test it was found to be more specific. The necessity to utilize virus-neutralization test systems for comparing FMD virus strains particularly for the purpose of vaccine selection is emphasized. The two dimensional microneutralization test has been applied to a study of comparing FMDV vaccine strains for Europe, South America, the Middle East and East Africa.

Differentiation between specific and nonspecific reactions of bovine sera and foot and mouth disease virus (FMDV) in immunodiffusion tests

The precipitating and neutralizing activities of normal bovine sera with FMDV were studied and compared. Twenty-two out of 79 normal bovine sera gave a positive reaction in micro neutralization tests with FMDV type O, while six did so with type A. In RID tests 32 sera were positive with type O and 28 with type A virus. Almost all of the 79 sera gave a positive reaction in the RID with trypsin treated virus of both types. After three to four fold concentration most sera also gave visible reactions in ID tests when tested against complete virus. When O virus was used the ID patterns produced by most normal sera clearly differed from those obtained with early and late convalescent sera from FMDV infected steers. When type A materials were employed this was also the case but to a lesser extent. The patterns obtained with concentrated normal sera showed, in general a strong line with trypsin treated virus and no line or a weaker one with complete virus. The substances in normal bovine sera precipitating trypsin treated O virus were different from those reacting with trypsinized virus of type A.

Neutralization of animal viruses

Various aspects of the interaction of bacterial viruses and antibody were studied by Andrewes and Elford in England. Similar studies, as well as studies on animal viruses, were carried out in Australia by Burnet and his colleagues. One result of their extensive studies, which were summarized in great detail, was the conclusion that, with respect to their interaction with antibody, bacterial and animal viruses were basically different. Specifically, the difference resided in the stability of the union of virus and antibody, whereas bacterial viruses formed stable complexes, animal viruses formed complexes that tended to dissociate readily. The introduction of animal cell cultures as host systems greatly aided in the study of animal viruses, with respect to fewer and more readily controlled variables, and by the use of the plaque assay in enhanced quantitative reliability. In 1956, Dulbecco et al. described the interaction of two animal viruses with their respective antibodies. The results of these studies led these investigators to conclude, among other things, that animal viruses, at least the two they studied, reacted with antibodies to form complexes that did not dissociate spontaneously. This interpretation was challenged by Fazekas de St. Groth and Reid. As more animal virus-antibody systems were studied by many investigators, there seemed to be a greater accord for irreversible, rather than reversible, interaction. For this reason, in this chapter it is assumed that there are no differences between bacterial viruses, as one category, and animal viruses, as a separate category, concerning their interaction with antibodies. Rather, differences, when they exist, are considered to be related to the viruses per se. Although this chapter is intended to survey the neutralization of animal viruses, occasional reference is made to the studies on bacterial viruses when these studies are pertinent and illuminating to the topic at hand.

Modeling and computer stimulation approach to the mechanism of foot-and-mouth disease virus neutralization assays

Block neutralization data since 1949 for the foot-and-mouth disease virus system have been analyzed in terms of a unified mass-action theory for computing the amounts of infectious complexes. Proof that infectious complexes contribute considerably to the assays was obtained by demonstrating a reduction in titer after an additional reaction with anti-Ig antibody before the assay. In the suckling-mice assay with intraperitoneal inoculation, both the data of others and our own on several types indicate that for IgG probably three of the unknown total number of critical sites on the virion must be available for infectivity and death. For IgM, just one of an unknown different total number of critical sites on the virion must be available. In tissue culture infectivity assays the minimum number is two or three, whereas in the bovine tongue assay it could be one or two, but probably two. The difficulties in establishing the at present unknown total numbers of neutralization sites to both IgG and IgM are considerable. However, by the simplest interpretation of the data, the number is estimated to be between 5 and 10 for IgG and perhaps just 1 for IgM. A speculation, consistent with the known virion architecture, is that just 1 of the 12 vertices is uniquely involved in infectivity and death, at least in the suckling-mice assay.

Preparation and immunogenicity of a purified influenza virus haemagglutinin and neuraminidase subunit vaccine

A vaccine was prepared containing the haemagglutinin and neuraminidase subunits from the A/Port Chalmers. 1/73 (H₃N₂) strain of influenza virus. The virus particles were disrupted with ammonium deoxycholate and the matrix protein, which was insoluble in this detergent, was removed by centrifugation. Following removal of deoxycholate, the haemagglutinin and neuraminidase subunits aggregated by their hydrophobic ends, forming mixed clusters. These were then freed from nucleocapsids by electrophoresis.

The haemagglutinin and neuraminidase subunits were as effective as intact inactivated virus (at equivalent concentration) in eliciting a late primary antibody response when injected in saline into rabbits.

In humans also, the subunits were as immunogenic as intact inactivated virus particles at equivalent concentration. Many people, however, responded only to the ‘common’ antigenic determinant(s) on the haemagglutinin subunit of Port Chalmers/73 virus and did not respond at all to the ‘specific’ determinant(s). Sera from these people contained antibodies which reacted equally as well with Hong Kong/68 virus as with the Port Chalmers/73 strain and none which reacted exclusively with the latter virus.

Immunoglobulins of the chicken antibody to Newcastle disease virus (Mukteswar and F strain)

The qualitative and quantitative development of chicken immunoglobulins in response to R2B (Mukteswar) and F strain of Newcastle disease virus was studied. One primary (R2B) and two secondary (R2B - R2B, F - R2B) vaccination trials were conducted. Sera was collected at weekly intervals and analyzed. There was an increase in total serum protein content in parallel to an increase in serum neutralizing (SN), hemagglutination inhibition (HI), and precipitating antibodies. The SN, HI and precipitating activities were detected both in IgM and IgG immunoglobulins when sera were treated with mercapto-ethanol. However, Sephadex G-200 fractionated sera showed only SN activity in the IgM fraction, whereas the IgG fraction showed both HI and SN activity. Serum IgM antibodies appeared during the first week following vaccination, then diminished, then rose again following secondary vaccination. Apparently, immunoglobulin induction and serological activities were not significantly influenced by the age of the chickens.

Marek's disease in Japanese quail -- a pathological, virological and serological study

Experimental studies were performed to see whether Japanese quail (Coturnix coturnix japonica) are susceptible to JM strain of Marek's disease virus (MDV). In three identical trials, a total of 120, one-day-old quail were inoculated intra-abdominally with 0.2 ml. of chicken blood infected with MDV (JM strain) and raised in FAPP isolators. Uninfected controls were inoculated with normal saline only and raised separately. During the 18-week post infection observation period, 65-80% of the infected quail died within six weeks, while the highest mortality in control groups was only 0-5%. In each trial, ocular lesions with or without unilateral or bilateral blindness and signs of torticollis were evident in a few quail after 10-14 weeks. Gross and microscopic lesions suggestive of MD were observed 14 days on. The most pronounced lesions were observed in lungs. Neural tissues were least affected. In general, females were more susceptible than males. MD-specific fluorescent and precipitating antigens were detected in different visceral tissues, buffy coat and cultured macrophages of infected quail. Fluorescent antigen appeared at 6-7 days after infection, whereas precipitating antigen appeared after 12-15 days. Viral (MDV) infectivity tests in cell cultures and bioassay in one-day-old chicks and quail demonstrated that infected quail become viremic around the seventh day post infection. A cytopathic agent similar to MDV was also isolated from quail. Neither Newcastle disease virus nor a bacterial agent was isolated from the quail. MD-specific fluorescent precipitating antibodies were present in the egg yolk and plasma of both infected sick and infected symptomless quail. The earliest detectable plasma MD antibody appeared in 14-21 days. Such findings were not observed in quail from parent stock and controls. Our studies demonstrated that Japanese quail are susceptible to JM strain of MDV.

Antibody-mediated elimination of malaria parasites (plasmodium berghei) in vivo

An infective preparation of extracellular blood forms (FP) of Plasmodium berghei was used to study some aspects of the interaction between protective antibodies and malaria parasites. FP but not infected erythrocytes (IRBC) were shown by the fluorescent antibody technique to be coated by antibodies after in vitro incubation with immune serum. Preincubation of both FP and IRBC with immune serum followed by their washing did not result in enhanced elimination of the parasites in vivo. However, FP preincubated with immune serum and subsequently washed were eliminated more efficiently than FP preincubated with normal serum if the preparations were injected with some immune serum. Such an increase in the efficiency of elimination was not detected with similarly pretreated IRBC. It is thus probable that protective antibodies acted in vivo against extracellular parasites rather than against parasites in erythrocytes. The interaction between parasites and antibodies may be of a highly reversible nature, and washing of the in vitro-treated parasites may cause elution of antibody from the sensitized parasites so that the amount of antibody on the parasite falls below the critical level required for in vivo elimination.