Conservation ofBabesia bovisSmall Heat Shock Protein (Hsp20) among Strains and Definition of T Helper Cell Epitopes Recognized by Cattle with Diverse Major Histocompatibility Complex Class II Haplotypes

Abstract

Babesia bovis small heat shock protein (Hsp20) is recognized by CD4؉ T lymphocytes from cattle that have recovered from infection and are immune to challenge. This candidate vaccine antigen is related to a protective antigen of Toxoplasma gondii, Hsp30/bag1, and both are members of the ␣-crystallin family of proteins that can serve as molecular chaperones. In the present study, immunofluorescence microscopy determined that Hsp20 is expressed intracellularly in all merozoites. Importantly, Hsp20 is also expressed by tick larval stages, including sporozoites, so that natural tick-transmitted infection could boost a vaccine-induced response. The predicted amino acid sequence of Hsp20 from merozoites is completely conserved among different B. bovis strains. To define the location of CD4 ؉ T-cell epitopes for inclusion in a multiepitope peptide or minigene vaccine construct, truncated recombinant Hsp20 proteins and overlapping peptides were tested for their ability to stimulate T cells from immune cattle. Both amino-terminal (amino acids [aa] 1 to 105) and carboxyterminal (aa 48 to 177) regions were immunogenic for the majority of cattle in the study, stimulating strong proliferation and IFN-␥ production. T-cell lines from all individuals with distinct DRB3 haplotypes responded to aa 11 to 62 of Hsp20, which contained one or more immunodominant epitopes for each animal. One epitope, DEQTGLPIKS (aa 17 to 26), was identified by T-cell clones. The presence of strain-conserved T helper cell epitopes in aa 11 to 62 of the ubiquitously expressed Hsp20 that are presented by major histocompatibility complex class II molecules represented broadly in the Holstein breed supports the inclusion of this region in vaccine constructs to be tested in cattle.

Molecular cloning of a small heat shock protein (sHSPII) from the cattle tick Rhipicephalus (Boophilus) annulatus salivary gland

“…This fact is supported by observation of Norimine et al [55] who studied the protective power of Babesia bovis HSP20 as a candidate vaccine [55]. They claimed that "the most immunostimulatory region of B. bovis Hsp20 for T helper cells from the cattle used in this study is the Nterminal region spanning amino acid 11 to 62".…”

Identification of Major Histocompatibility Complex Restriction and Anchor Residues of Foot-and-Mouth Disease Virus-Derived Bovine T-Cell Epitopes

“…6). This is supported by recent publications showing that DQ molecules in cattle are relevant for peptide presentation to T helper cells in immune responses against FMDV-derived peptides (15), Babesia bovis (26), and Anaplasma marginale (6). Furthermore, FIG.…”

Adaptive immunity to Anaplasma pathogens and immune dysregulation: Implications for bacterial persistence

“…In cattle, the MSP2-specific antibody response is predominantly directed toward the hypervariable region rather than the flanking conserved regions [86, 87]. This is not surprising, as the hypervariable region is predicted to be surface exposed [86] and antigenic variation is detected under conditions of immune pressure and selection, which would not apply to surface exposed conserved sequences. Evasion of the anti-MSP2 antibody response by newly emerging variants during persistent infection was documented for A. marginale [49] and for A. phagocytophilum in sheep [7, 88].…”

“…As new antigenic variants of MSP2 or MSP3 arise during persistent infection, T cells may be continually primed to these new variants, which are then suppressed or deleted as antigen load increases. We have shown that both hypervariable as well as conserved regions of MSP2 contain CD4 + T cell epitopes [86, 90]. During persistent infection, there may also be continuous priming and expansion of CD4 + T cells to epitopes on subdominant outer membrane proteins [61].…”