Assessment of T lymphocyte responses induced by parasite antigens

The epidemiology and control of swine parasites. Immunity and vaccines

This article discusses the status of two experimental swine helminthic vaccines and how further knowledge of parasite biochemistry and swine immunology and the application of techniques of modern biotechnology may affect their future development.

Ascaris suum infection in pigs sensitizes lymphocytes but suppresses their responsiveness to phytomitogens

The effect of Ascaris suum infection and treatment with fenbendazole on the blastogenic response of peripheral blood lymphocytes to A. suum antigens and to three phytomitogens was assayed by the lymphocyte transformation technique. Repeated infections with A. suum led to the development of sensitized lymphocytes primarily responding to egg hatching fluid antigen. Treatment with fenbendazole decreased the number of specific sensitized lymphocytes, but favorably increased the resistance of pigs to reinfection. Immunity to reinfection did not correlate with the strength of the blastogenic response to A. suum antigens. Repeated infection with A. suum negatively affected the development of the blastogenic response to phytomitogens in the pigs, leading to a partial depression of the responsiveness of lymphocytes and to the partial suppression by serum. Responses to pokeweed mitogen were affected more than the responses to concanavalin A and phytohemagglutinin.

Limiting dilution analyses for the quantification of cellular immune responses in bovine ostertagiasis

A sensitive limiting dilution analysis (LDA) was used to quantitate the local and systemic cellular immune response of cattle after immunization with keyhole limpet hemocyanin (KLH) and infection with Ostertagia ostertagi. The assay measures the proliferative response of bovine T-cells after in vitro stimulation with antigen. Interleukin 2 activity was supplied by supernates from mitogen-stimulated bovine peripheral blood lymphocytes (PBL) and accessory cell function was in the form of irradiated autologous PBL. The assay measures the response of a single cell and was most easily demonstrated in the lymph nodes draining the site of antigen inoculation. Comparison of cell frequencies and maximal responses generated in conventional proliferative assays showed several differences between the two assays. First, after antigen injection, the highest cell frequencies were seen in the draining lymph nodes within 3 days, and decreased by 10 days post-immunization. In contrast, in mass cultures maximal stimulation was not seen until 7-10 days after injection, but remained high up to 4 weeks after immunization. Second, at 17 days post-infection, a time of eruption of the parasite from the gastric glands, high frequencies of inducible cells were demonstrated by LDA in all lymphoid populations tested. In contrast, low levels of proliferation were seen in mass cultures. The reasons for these differences may include different sensitivities to suppression or more stringent requirements for specificity between the two assays. Finally, it was found that immunologically naive calves have relatively high frequencies of Ostertagia-specific cells in PBL, and that after infection these frequencies decrease. These results indicate either active suppression of the potential anti-Ostertagia response or an extra-vascularization of these cells to the site of infection.

Biotechnology in the development of vaccines for animal parasites

Attempts to develop vaccines for protozoan and helminth parasites of livestock have been generally unproductive. Difficulties have been encountered in identifying antigens which induce protective immune responses and in obtaining sufficient quantities of antigens for vaccine trials. Use of monoclonal antibody and genetic engineering technologies provides the necessary tools to overcome these problems. Application of these technologies in animal parasitology should provide for significant breakthroughs in vaccine development.

Suppression of antigen- and mitogen-induced proliferation of bovine lymphocytes by excretory-secretory products of Oesophagostomum radiatum

Excretory-secretory products (ESP) isolated from in vitro-grown stage-3 to -4 larvae of Oesophagostomum radiatum were found to inhibit both the in vitro antigen-specific proliferation of keyhole limpet hemocyanin- and ovalbumin-primed lymphocytes and the proliferation induced by the T-cell mitogen concanavalin A. As little as 50 ng of ESP protein per culture resulted in 50% reductions of subsequent proliferative responses. Antigen-induced responses were 100 to 1,000 times more sensitive to inhibition than were mitogen-induced responses. The inhibitory activity was found to affect the induction of proliferation as evidenced by the observation that complete inhibition was seen when ESP were added to cultures within the first 24 h. ESP were found to have no inhibitory activity when added 72 h after the initiation of the cultures. The inhibition was not a result of a direct action upon macrophages because pulsing of adherent cells with ESP had no more effect on a subsequent proliferative response than did a pulsing of the culture vessel itself. The inhibitory activity eluted from high-pressure liquid chromatography columns in the same fractions as protein standards with molecular weights of 25,000 to 35,000. Of special interest is the fact that this inhibitor of the expansion of immunoreactive clones of lymphocytes is found associated with the stages of parasites most intimately associated with host tissues, namely larval stages 3 and 4.

Porcine interleukin 2: parameters of production and biochemical characterization

Interleukin 2 (IL2) or T cell growth factor (TCGF) has been characterized in a number of species but not in porcines. Porcine IL2 was detected in supernates (SN) of cultures of pig lymphocytes by: 1) the stimulation of the IL2-sensitive murine T cell line, CT6; 2) a costimulator assay involving porcine thymocytes; and 3) by the in vitro maintenance of antigen or mitogen-induced porcine lymphoblastoid cells. Porcine IL2 production by pig lymphocytes was induced by the mitogens Concanavalin A (Con A) Phytohemagglutiniin (PHA), and Pokeweed mitogen (PWM), but not by lipopolysaccharide (LPS). IL2 activity was demonstrated in the SN of mitogen-stimulated lymphocyte cultures as early as 24 hr after initiation of culture, reached peak levels at 48 hr, and decreased by 72 hr. Mitogens induced IL2 secretion by pig peripheral blood mononuclear cells, lymph node cells, and spleen cells, but not thymus cells. The cells responsible for IL2 production are presumptive T cells because: 1) they are nylon wool non-adherent; and 2) are non-surface-Ig bearing. In contrast, SN from cultures of surface Ig-positive cells had minimal IL2 activity. Porcine IL2 resembles rat and human IL2 in that it has an apparent molecular weight of approximately 15,000, and does not bind to DEAE-cellulose (DE-52) ion exchange columns equilibrated in 0.05 M sodium phosphate buffer (pH 7.6).