Immunological profiles of Bos taurus and Bos indicus cattle infested with the cattle tick, Rhipicephalus (Boophilus) microplus

Abstract

The cattle tick, Rhipicephalus (Boophilus) microplus, is a major threat to the improvement of cattle production in tropical and subtropical countries worldwide. Bos indicus cattle are naturally more resistant to infestation with the cattle tick than are Bos taurus breeds, although considerable variation in resistance occurs within and between breeds. It is not known which genes contribute to the resistant phenotype, nor have immune parameters involved in resistance to R. microplus been fully described for the bovine host. This study was undertaken to determine whether selected cellular and antibody parameters of the peripheral circulation differed between tick-resistant Bos indicus and tick-susceptible Bos taurus cattle following a period of tick infestations. This study demonstrated significant differences between the two breeds with respect to the percentage of cellular subsets comprising the peripheral blood mononuclear cell population, cytokine expression by peripheral blood leukocytes, and levels of tick-specific immunoglobulin G1 (IgG1) antibodies measured in the peripheral circulation. In addition to these parameters, the Affymetrix bovine genome microarray was used to analyze gene expression by peripheral blood leukocytes of these animals. The results demonstrate that the Bos indicus cattle developed a stabilized T-cell-mediated response to tick infestation evidenced by their cellular profile and leukocyte cytokine spectrum. The Bos taurus cattle demonstrated cellular and gene expression profiles consistent with a sustained innate, inflammatory response to infestation, although high tick-specific IgG1 titers suggest that these animals have also developed a T-cell response to infestation.

FIG. 1.

Percentage of each cellular subset comprising the PBMC population of Holstein-Friesian (black) and Brahman (white) cattle. Results are presented as the breed means of three time points with standard deviations from the group means. Asterisks denote a significant difference (P < 0.01) between the Holstein-Friesian and Brahman cattle.

FIG. 2.

Flow cytometric displays of peripheral blood lymphocytes from a representative Holstein-Friesian animal (subpanels A to C) and a representative Brahman animal (subpanels D to F). (a) CD4⁺ cells; (b) CD14⁺ cells; (c) CD25⁺ cells; (d) MHCII⁺ cells; (e) WC1⁺ cells. Dot plots in subpanels A and D depict forward scatter versus side scatter light data. The mononuclear lymphocyte population is gated in red. Subpanels B and E depict the isotype-labeled lymphocyte population on a dot plot of FITC fluorescence versus side scatter light data. Subpanels C and F depict the gated lymphocyte population labeled with the respective antibody specific for the cell surface antigen.

FIG. 3.

IgG1 antibody levels specific for tick antigen extracts of Holstein-Friesian (black) and Brahman (white) cattle. Results are presented as breed means of three time points with standard deviations from the group means. Holstein-Friesian animals had significantly (P < 0.001) higher levels of IgG1 antibodies specific for all tick antigen extracts than did Brahman animals, as indicated by the asterisks.

FIG. 4.

Cytokine/chemokine receptor expression by WBCs of Holstein-Friesian (black) and Brahman (white) cattle. Results are presented as breed mean normalized expression values with standard deviations from the group means. Asterisks denote significant differences between the breeds.

FIG. 5.

MAS5 heat map plot of the top 100 (most significant) DE genes clustered using hierarchical clustering. Affymetrix identifications are listed with their corresponding gene symbol or “NA” if no gene assignment is available. For further information on gene names, expression changes, and significance values, see Table S1 in the supplemental material or the supplementary analysis file available through the accession number GSE13725 at the GEO website.

FIG. 6.

Ontology analysis of 224 annotated DE genes in WBCs of Brahman and Holstein-Friesian cattle. The y axis lists the major biological processes represented by the 224 DE genes, and the x axis indicates the percentages of DE genes involved in the respective GO biological process. (Note that a gene may be involved in more than one GO category and thus the total percentage is more than 100.)