Abstract:
Theileria parva is a protozoan parasite that causes the disease East Coast fever in
cattle leading to major economic losses in Eastern and Southern Africa including
Kenya. A live vaccine against the parasite exists normally administered by
subcutaneously injecting live parasites simultaneously with long acting
oxytetracycline antibiotic. Nevertheless, challenges such as requirement of cold
chain storage, difficult production procedures and the live vaccine being potentially
lethal, makes it vital to explore other vaccine alternatives including inactivated
vaccines and recombinant subunit vaccines. This study seeks to provide scientific
output that will help in continued effort to develop new vaccine strategies. The
mainstay of this exploration is a much better understanding of the CD8+ T-cells
which are believed to be the main line of defence in East Coast fever. Hence it is
essential to generate a profile of the T. parva specific CD8+ killer cells. In this study
the phenotypic and functional characterization of these T. parva specific CD8+ Cells
was determined by; i) Expression of surface and intracellular effector biomarkers by
FACS analysis, ii) Degree of cell activation by secretion of interferon γ by ELISPOT
analysis, and iii) Cytotoxic potential of CD8+ T-cells against T. parva infected cells
was done in comparison to γδ T-cells. Blood samples were taken from the A18
BoLA type experimental cattle immunized with the live sporozoite vaccine. Bulk
CTL and purified CTL cell lines were then generated from the experimental animals.
From this study various surface and intracellular biomarkers found on T. parva
specific CD8+ T-cells were identified. These included; CD2, CD3, CD4, CD25,
CD44, CD45RO, CD62L, CD71, WC1, γδTCR, Perforin, FasL. Two of these
markers indicated the presence of another T cell subsets γδ T-cells (WC1 and γδ
TCR). It was observed from three cell lines (BF076, BF077, and BF079) that the
degree of activation of CD8+ T-cells to T. parva antigen Tp1
214-224
as compared to γδ
T-cells was not significantly different (P > 0.05). The CD8+ T-cells exhibited
significant cytotoxicity to T. parva infected lymphocytes while the γδ T-cells
exhibited no measurable cytotoxicity. The study revealed that two of the activation
markers, perforin and CD25 are possible surrogate markers for cytotoxicity, which is known to correlate with immunity to ECF infection. This study provided additional
tools for characterizing cell-mediated immunity to T. parva induced by recombinant
parasite antigens.
