Bea Mertens

Immune Response of Cattle Infected with African Trypanosomes

Trypanosomosis is the most economically important disease constraint to livestock productivity in sub-Saharan Africa and has significant negative impact in other parts of the world. Livestock are an integral component of farming systems and thus contribute significantly to food and economic security in developing countries. Current methods of control for trypanosomosis are inadequate to prevent the enormous socioeconomic losses resulting from this disease. A vaccine has been viewed as the most desirable control option. However, the complexity of the parasites antigenic repertoire made development of a vaccine based on the variable surface glycoprotein coat unlikely. As a result, research is now focused on identifying invariant trypanosome components as potential targets for interrupting infection or infection-mediated disease. Immunosuppression appears to be a nearly universal feature of infection with African trypanosomes and thus may represent an essential element of the host-parasite relationship, possibly by reducing the hosts ability to mount a protective immune response. Antibody, T cell and macrophage/monocyte responses of infected cattle are depressed in both trypanosusceptible and trypanotolerant breeds of cattle. This review describes the specific T cell and monocyte/macrophage functions that are altered in trypanosome-infected cattle and compares these disorders with those that have been described in the murine model of trypanosomosis. The identification of parasite factors that induce immunosuppression and the mechanisms that mediate depressed immune responses might suggest novel disease intervention strategies.

Cloning of a cDNA encoding bovine erythropoietin and analysis of its transcription in selected tissues

A bovine cDNA encoding erythropoietin (Epo) was isolated by polymerase chain reaction (PCR) amplification and screening of a bovine kidney cDNA library. The sequenced cDNA has a length of 1312 bp and an open reading frame that encodes a predicted 192-amino-acid (aa) protein, including a putative signal sequence of 25 aa. A mature protein of 167 aa (18.4 kDa) results upon cleavage of the putative signal peptide. The deduced bovine mature Epo peptide exhibits 96, 88, 83, 82 and 79% sequence identity to that of sheep, swine, human, monkey and rat, respectively. The expression of the bovine Epo gene in tissues from a severely anemic calf, bovine fetus and a healthy steer was analysed by a competitive RT-PCR method. In kidneys of the severely anemic calf, Epo mRNA levels increased 60-fold relative to that from the kidneys of the healthy steer. Epo mRNA levels were threefold higher in the liver of the bovine fetus than that in its kidneys. Low levels of Epo transcripts were detected in RNA from spleen of the severely anemic calf and the bovine fetus. No Epo transcripts were detectable in spleen from the healthy steer.

Transcription of the unique ruminant class II major histocompatibility complex-DYA and DIB genes in dendritic cells.

Dendritic cells (DC) constitute the most effective immune cell population for priming and recalling T cell responses to foreign antigens. DC patrol the peripheral tissues collecting foreign antigen for subsequent presentation by classical class II MHC molecules to T cells in the draining lymph nodes. Since the description of the DYA and DIB class II MHC genes, which are unique to ruminants, no transcript or protein have been reported. Here we provide evidence that these genes are transcribed in cattle and that paired transcription is restricted in afferent lymph to a functionally distinct population of DC. Analysis of lymph node, lung and thymus suggests that tissue DC also transcribe both genes. Cytokine‐induced differentiation of cultured monocytes to a DC phenotype is linked with induction of both DYA and DIB transcription. This is consistent with an association of their products with the potent antigen presenting capacity of these cells in cattle.

Cloning, sequence and mRNA expression of bovine interleukin-16.

A lambda gtll cDNA library was constructed using mRNA isolated from Theileria parva-infected bovine lymphocytes. Sequencing of random clones of this library resulted in the identification of a cDNA encoding bovine interleukin-16 (IL-16). The cDNA has an open reading frame of 1134 bp, and a 3′ untranslated region of 275 nucleotides with a polyadenylation signal 16 bases upstream from the poly (A) tail. The protein predicted by the cDNA sequence contains 378 amino acids and the level of amino acid homology with the corresponding part of human precursor IL-16 is 79%. No information is available about the tissue distribution of IL-16 in cattle, therefore we investigated the expression of IL-16 mRNA in bovine lymphoid tissues by reverse-transcription polymerase chain reaction assays. To investigate the potential of IL-16 as an immunoregulatory molecule we also analysed IL-16 mRNA expression in CD4+ and CD8+T-cell clones derived from T. parva-immunised cattle.

Bovine stem cell factor: Production of a biologically active protein and mRNA analysis in cattle infected with Trypanosoma congolense

The cDNA coding for the soluble form of bovine stem cell factor (boSCFAla165) was cloned and recombinant protein was produced in bacteria as a histidine tagged-protein. The protein was purified from the inclusion bodies in one step by metal chelation chromatography under denaturing conditions. Recombinant bovine SCF was shown to act synergistically with interleukin 3 (IL-3) and erythropoietin (EPO) in stimulating the growth of bone marrow progenitor cells such as colony forming units-granulocyte macrophage (CFU-GM) and burst forming units-erythroid (BFU-E). Analysis of SCF mRNA expression by reverse transcription-polymerase chain reaction (RT-PCR) revealed that the transcripts were detectable in bone marrow, lymph nodes and spleen of cattle, and that the level of transcription was upregulated in lymph nodes of cattle infected with Trypanosoma congolense. Two isoforms of SCF mRNA were amplified by RT-PCR. The availability of recombinant bovine SCF provides a valuable tool for studying the role of SCF in the development, growth and differentiation of bovine hematopoietic cells.