Immunoglobulin-bearing cells in giardiasis

Immune effector responses to an excretory-secretory product of Giardia lamblia

The prior immunisation of mice with purified excretory-secretory product (ESP) led to a complete failure of Giardia lamblia colonisation following challenge inoculation of these animals with trophozoites. The prior immunisation of mice with ESP resulted in a significant stimulation of local immunity as evidenced by a significant enhancement of T helper/inducer activity along with a significant increase in immunoglobulin A-bearing cells. Further, the presence of anti-ESP antibodies in the serum of immunised as well as immunised-challenged animals indicated the stimulation of the systemic lymphoid system. This suggests that the ESP is highly immunogenic and it could be one of the major antigens of G. lamblia responsible for protection against the infection.

Sequential changes of lamina propria immunoglobulin-containing cells in immune intact and immunosuppressed mice infected with Giardia lamblia

Following Giardia lamblia infection in immune intact NMRI mice, increased numbers of IgM-containing cells and decreased numbers of IgA containing cells were noticed in the lamina propria during the establishment (3-5 days) and acute (9-11 days) phases of infection. The decline in IgM-containing cells during the clearance phase of infection (17-21 days post-infection) was accompanied by an increase in IgA and IgG-containing cells. Our data suggest that the locally synthesized antibodies, especially of the IgA class, play a significant immunodulatory role in the clearance of G. lamblia infection from the gut. Mice immunosuppressed using rabbit anti-mouse lymphocyte serum or dexamethasone had significantly reduced numbers of IgA and IgG-containing cells during all phases of infection and higher parasite loads in their jejunum. It appears that one of the reasons for increased severity and chronicity of G. lamblia infection is the decrease in immunoglobulin-containing cells in the gut.

Mechanism of killing of Giardia lamblia trophozoites by complement

Only antibodies of the IgM class support the lytic effect of complement on Giardia lamblia (GL). We sensitized GL trophozoites (SGL) at 4 degrees C with serum containing anti-GL antibodies or IgM purified from this serum, and either normal human serum (NHS), complement 2-deficient human serum (C2d-HS), or C4-deficient guinea pig serum was used as source of complement. SGL were killed by NHS (86%) and by the deficient sera (50 and 40%, respectively), suggesting activation of the alternative pathway. However, the reaction was inhibited by Mg-EGTA. These observations led to studies of the role of C1. The lytic effect of NHS and C2d-HS on SGL was abolished by immunochemically depleting C1 from these sera, and reconstituted by adding purified C1q plus C1r and C1s. Factor B-depleted C2d-HS also lost its capacity to mediate killing, but reconstitution with factor B led to a dose-dependent increase in the killing of SGL. We next investigated the participation of the membrane attack complex in this system. SGL carrying C5b to C7 were lysed when incubated with C8 alone (56%); the addition of C9 further increased killing (98%), while C9 in the absence of C8 had no effect. We concluded that although activation of the classical pathway produces lysis of SGL, lysis may also proceed through a unique pathway of complement activation that requires C1 and factor B, but is independent of C4 and C2. Lysis of SGL can be accomplished by C5b to C8 in the absence of C9.

Comparative studies of inflammatory responses in susceptible and resistant mice infected with Giardia muris

A comparative assessment of in-vivo and in-vitro inflammatory responses in mice which are susceptible (A/J) and resistant (B10.A) to Giardia muris was made. B10.A mice which have the ability to eliminate the parasites exhibited a greater capacity to recruit cells into the peritoneal cavity after thioglycollate injection, when compared to A/J mice. The recruitment of inflammatory cells into the peritoneal cavity by B10.A mice was higher on day 15 (acute phase) and on day 60 (elimination phase) of the infection. Quantitative differences in inflammatory responses of A/J and B10.A mice in vivo were related to the functional differences in macrophage phagocytosis and chemotaxis in vitro. Macrophages from the resistant B10.A mice were more phagocytically active and were more chemotactically responsive during both acute and elimination phases of the infection, compared to those from the susceptible A/J mice. There was a relationship between the capacity of A/J and B10.A mice to mount inflammatory responses and the ability of these strains of mice to control the infection with G. muris.

Diagnosis of giardiasis by specific IgM antibody enzyme-linked immunosorbent assay

An enzyme-linked immunosorbent assay (ELISA) was used to detect serum IgM and IgG antibodies against Giardia in fifty-two patients with diarrhoea from the United Kingdom and south India. Serum anti-Giardia IgM responses occurred in patients with giardiasis; in two of three patients studied longitudinally IgM levels had fallen to normal 2-3 weeks after treatment. At serum dilutions of 1/200 to 1/400 there was almost complete separation of ELISA readings between patients with Giardia and Giardia-free controls; the sensitivity and specificity of the ELISA were both 96%. Serum anti-Giardia IgG was detected in patients and controls but was unable to distinguish current from previous infection.

Opsonization in vitro of Giardia lamblia trophozoites

The ability of peritoneal rabbit macrophages from immunized and nonimmunized animals to phagocytose Giardia lamblia trophozoites in the presence of serum was studied and compared in an in vitro system. The rabbits which served as the source of immune serum and macrophages were injected repeatedly at multiple sites (intramuscularly, subcutaneously, and intradermally) with a mixture of G. lamblia trophozoites and Freund complete adjuvant. In the presence of normal rabbit serum, a low level of phagocytosis of Giardia trophozoites by normal and immune macrophages was observed. In the presence of hyperimmune rabbit serum, an increased phagocytic activity of both types of macrophages occurred. The opsonic activity was similar whether whole serum or purified immunoglobulin G was used and whether or not these were heat inactivated. G. lamblia trophozoites in suspension were shown to be agglutinated in the presence of hyperimmune serum. Tests employing serial dilutions of hyperimmune serum resulted in a parallel loss of opsonifying and agglutinating activities. It is suggested that opsonization in vivo may play a role in the ability of the host to limit infection by these organisms.