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Infect. Immun., 04 1995, 1258-1262, Vol 63, No. 4
EL Taracha, BM Goddeeris, SP Morzaria and WI Morrison
Class I major histocompatibility complex-restricted parasite-specific
cytotoxic T lymphocytes (CTL) are known to be a major component of the
bovine immune response to the protozoan parasite Theileria parva, but
formal proof for their role in protection of cattle against infection with
T. parva has been lacking. Animals immunized with one stock of T. parva
show variations in the degree of protection against heterologous challenge
and also in the parasite strain specificity of their CTL responses. The
present study investigated the relationship of strain specificity of CTL
responses and cross-protection in an effort to verify the role of CTL in
protection. The parasite strain specificity of the CTL responses generated
in 23 cattle immunized with either of two immunologically distinct parasite
populations was examined, and the susceptibility of individual cattle to
challenge with the heterologous parasite population was determined. The
frequency of stock-specific or cross-reactive CTL precursor cells (CTLp) in
individual animals was measured by a limiting-dilution microassay. A
proportion of animals immunized with either parasite exhibited
cross-reactive CTLp, whereas CTLp detected in the remaining animals were
specific for the homologous parasite. On challenge with the heterologous
stock, those animals with cross-reactive CTLp were solidly protected while
those with strain- specific CTLp showed moderate to severe reactions,
although many of them recovered. The finding of a close association between
strain specificity of the CTL response and protection against challenge
provides strong evidence that CTL are important in mediating immunity.
Copyright © 1995, American Society for Microbiology
Parasite strain specificity of precursor cytotoxic T cells in individual animals correlates with cross-protection in cattle challenged with Theileria parva
International Laboratory for Research on Animal Diseases (ILRAD), Nairobi, Kenya.
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