Passive transfer of maternal immunity in the dromedary (Camelus dromedarius), involvement of heavy chain antibodies

Development of a bispecific Nanobody anti-F17 fimbria as a potential therapeutic tool

Pathogenic strains of Escherichia coli F17+ are associated with various intestinal and extra-intestinal pathologies, including diarrhea, and result in significant animal mortality. These infections rely on the expression of virulence factors, such as F17 fimbriae, for adhesion. F17 fimbriae form a protective layer on the surface of E. coli bacteria, consisting of a major structural subunit, F17A, and a minor functional subunit, F17G. Because of the evolution of bacterial resistance, conventional antibiotic treatments have limited efficacy. Therefore, there is a pressing need to develop novel therapeutic tools. In this study, we cloned and produced the F17G protein. We then immunized a camel with the purified F17G protein and constructed a VHH library consisting of 2 × 109 clones. The library was then screened against F17G protein using phage display technology. Through this process, we identified an anti-F17G nanobody that was subsequently linked, via a linker, to an anti-F17A nanobody, resulting in the creation of an effective bispecific nanobody. Comprehensive characterization of this bispecific nanobody demonstrated excellent production, specific binding capacity to both recombinant forms of the two F17 antigens and the E. coli F17+ strain, remarkable stability in camel serum, and superior resistance to pepsin protease. The successful generation of this bispecific nanobody with excellent production, specific binding capacity and stability highlights its potential as a valuable tool for fighting infections caused by pathogenic E. coli F17+ strain.

Failure of Passive Transfer in Camel Calves: 4 Cases (2010-2019)

Failure of passive transfer is a management concern for all ruminant species, but is not well described in the literature for camel calves. This case series presents four camel calves (Camelus dromedarius and Camelus bactrianus) referred to a North American veterinary teaching hospital for diagnosis and management of failure of passive transfer. Diagnostics utilized included hematology, serum biochemistry, and immunologic methods as described for crias. Management included antimicrobial, anti-inflammatory, and plasma transfusion therapies. Three of the four calves survived to discharge, and common diagnostic practices such as evaluation of total solids, total protein, immunoglobulin G, and sodium sulfite appear to be correlate to passive transfer status in these four calves. Xenotransfusion with llama plasma was well tolerated by two calves, and xenotransfusion with bovine plasma was well tolerated by an additional calf in this study. An additional work is necessary to develop validated breakpoints for diagnosis of passive transfer status in camel calves.

Recent Advances in Camel Immunology

Camels are domesticated animals that are highly adapted to the extreme desert ecosystem with relatively higher resistance to a wide range of pathogens compared to many other species from the same geographical region. Recently, there has been increased interest in the field of camel immunology. As the progress in the analysis of camel immunoglobulins has previously been covered in many recent reviews, this review intends to summarize published findings related to camel cellular immunology with a focus on the phenotype and functionality of camel leukocyte subpopulations. The review also describes the impact of different physiological (age and pregnancy) and pathological (e.g. infection) conditions on camel immune cells. Despite the progress achieved in the field of camel immunology, there are gaps in our complete understanding of the camel immune system. Questions remain regarding innate recognition mechanisms, the functional characterization of antigen-presenting cells, and the characterization of camel NK and cytotoxic T cells.

Investigation of total immunoglobulin G concentration, heavy chain antibody levels, and neutrophil to lymphocyte ratio in female camels and their newborn calves

Camels belong to a group of animals, where the structure of placenta does not allow intrauterine transfer of maternal immunoglobulins to the fetus and maternal immunity is exclusively transferred by colostrum to the newborn calf. There are few studies on the passive transfer of maternal immunity in the dromedary camel. This study determined total immunoglobulin G concentration, heavy chain antibody (HCAbs) levels, and neutrophils to lymphocytes ratio (NLR) in female camels and their newborn calves. For this, samples were collected from nine she-camels (blood and colostrum) and their calves (blood). IgG concentration and HCAb level were determined in mother serum and colostrum as well as in calf serum using ELISA. The NLR was calculated after the estimation of relative fractions of neutrophils and lymphocytes in collected blood samples using a blood cell analyzer. Both IgG and HCAbs were higher concentrated in camel colostrum than in mother serum. At parturition and before the first colostrum intake, calf serum did not contain any measurable concentration of IgG and only low levels of HCAbs. After colostrum consumption, a rise in IgG and HCAb levels was observed in calf serum. For total IgG, a minimum was reached on day 30 postnatum. While a significant increase in IgG concentration was seen on day 60 postnatum, no significant rise was measured in HCAbs at that age. Only post-colostrum IgG levels in calf serum correlated positively with IgG levels in mother colostrum. Directly after birth, newborn calves showed significantly higher NLR than their mothers. This indicates a pro-inflammatory nature of the calf immune response. The decrease of the NLR on day 60 postnatum may argue for the maturation of the calf immune response at this age.

Leukocyte populations and their cell adhesion molecules expression in newborn dromedary camel calves

Background and Aim

Different properties of the newborn immune system have been characterized in many species. For the newborn camel calf, however, the phenotype and composition of blood leukocytes have so far not been evaluated. The current study aimed to analyze the distribution of leukocyte subpopulations and their expression pattern of cell adhesion molecules in newborn and adult dromedary camels.

Materials and Methods

Blood samples were collected from 17 newborn camel calves and 32 adult camels. For each sample, total leukocytes were separated and analyzed for their composition and cell adhesion molecules expression by flow cytometry.

Results

In comparison to adult camels, newborn camel calves had higher leukocyte numbers and higher numbers of neutrophils, monocytes, and lymphocytes but lower numbers of eosinophils in their blood. Among the lymphocyte populations in calves, the fractions of B cells and γ^δ T cells were elevated when compared to adults, whereas CD4-positive T cells were reduced. The comparison between camel calves and adult camels revealed significantly lower expression of the cell adhesion molecules CD11a, CD11b, and CD18 on granulocytes, monocytes, and lymphocytes in calves.

Conclusion

Newborn camel calves show a distinct composition and phenotype pattern of blood leukocytes when compared to adult camels. The observed rise in many leukocyte populations in calf blood may be due to reduced migratory activity in calf leukocyte populations.