Adoptive transfer of immunity inGiardia lambliainfection in mice

Immune response to Giardia duodenalis

The intestinal protozoan Giardia duodenalis is a widespread opportunistic parasite of humans and animals. This parasite inhabits the upper part of the small intestine and has a direct life cycle. After ingestion of cysts, which are the infective stage, the trophozoites emerge from the cysts in the duodenum and attach to the small intestinal mucosa of the host. Since the migration of trophozoites from the lumen of the intestine into surrounding tissues is an unusual occurrence, the immune response to Giardia remains localized. The identification of antigens that play a role in acquired immunity has been difficult because of the occurrence of antigenic variation and because, Giardia being an ubiquitous organism, it is possible that the antigenic profiles of isolates from different geographic areas will vary. Innate-immunity mechanisms play a role in the control and/or severity of the infection. Both humoral and cell-mediated immune responses play a role in acquired immunity, but the mechanisms involved are unknown. A variety of serological assays have been used to detect circulating antibodies in serum. Because of the biological characteristics of the parasite and the lack of suitable antigens, the sensitivity of serological assays remains poor. On the other hand, detection of antigens in feces of infected patients has met with success. Commercial kits are available, and they are reported to be more sensitive than microscopic examination for the detection of giardiasis on a single specimen.

Human cellular immune response to Giardia lamblia

Human peripheral blood mononuclear cells (PBMC) from two individuals experimentally and one naturally infected with Giardia lamblia responded strongly (in an in vitro lymphocyte proliferation assay) to both heterologous and homologous (parasite origin) G. lamblia antigen stimuli. Proliferative responses to specific antigens as determined by T-cell blotting were due to Giardia T-cell epitopes mostly present in antigens lower than Mr 85,000 and 31,000 in isolates PM and GS/M-H7, respectively. Additionally, Il-2 production of PBMC respective to T lymphocyte subsets under antigen stimulation were determined in one selected patient. Proliferative and lymphokine responses could be associated with CD4+ PBMC depleted of CD8+ T cells and not with PBMC depleted of CD4+ T cells. These preliminary results suggest the initiation of larger studies addressing questions of cell-mediated immune response and the role of lymphokines in human giardiasis.

Kinetics of intraepithelium and lamina propria lymphocyte responses during Giardia lamblia infection in mice

The responses of intestinal T-cell subsets and immunoglobulin containing cells were assessed during the course of experimental Giardia lamblia infection in inbred NMRI mice. Quantitation of T-cell subsets in intraepithelium (IEL) and lamina propria (LPL) revealed increased influx of Lyt 2.2+ (suppressor/cytotoxic) T cells and Thy 1.2+ T cells during the establishment (3-5 days post-inoculation) and peak (9-11 days post-inoculation) phases of infection. The influx of these cells reduced as the parasite load declined. In contrast, no significant change was noticed in lamina propria and intraepithelial L3 T4+ (helper/inducer) T cells during the establishment or acute phases. However, these cells increased significantly in the decline phase (17-21 days post-inoculation) of infection. The lamina propria IgA-containing cells significantly declined during the establishment and acute phases of infection, and increased significantly as the parasite load in the jejunum declined. Helper/inducer ratios of 0.4 for IEL and 2.0 for LPL accompanied the decline of G. lamblia trophozoites in the gut. Our data thus suggest that induction of helper/inducer T cells during the decline phase of infection concomitant with an increase in lamina propria IgA-containing cells resulted in elimination of G. lamblia trophozoites from the gut.

Plasma membrane associated antigens of trophozoites of axenic Giardia lamblia

Plasma membrane isolated from axenically grown Giardia lamblia (Portland 1 strain) by treatment with a membrane stabilizing agent followed by osmotic stress and manual sheer showed a significant enrichment of the membrane bound marker enzymes CA++ATPase/Mg++ATPase. Crossed immunoelectrophoresis (CIE) was used to identify membrane antigens. 11 major peaks were detected in CIE profiles of the whole trophozoites. 6 major peaks were detected in CIE profiles of the membrane preparation. 2 surface membrane peaks with relative mobilities of 0.10 (peak 2) and 0.70 (peak 6) were identified by absorption studies. Peak 2 had a molecular mass of 82 kDa whereas peak 6 had a molecular mass of 56 kDa. The monospecific antiserum raised against the surface antigens of strain Portland 1 with molecular masses of 82 kDa and 56 kDa revealed the existence of identical antigens on 2 other isolates (Isr & WB) of G. lamblia.