Opsonic requirements for the respiratory burst of neutrophils against Giardia lamblia trophozoites

BACKGROUND: Giardia lamblia is an important cause of parasitic diarrheal disease worldwide. Occasionally, polymorphonuclear neutrophils (PMNs) may participate as effector cells against Giardia lamblia. The present study was performed in order to examine the role of specific antibody and complement components in promoting the respiratory burst (RB) of PMNs against Giardia lamblia. METHODS: PMNs from human adult volunteers were incubated with Giardia trophozoites in the presence of non-immune (NS) or hyperimmune (HS) serum (anti-Giardia titer, >1:1024). Adherence was scored visually on coverslide after staining with Giemsa. The ability of Giardia to trigger the oxidative response of PMNs was measured by the anion superoxide (O2(-)) production using a cytochrome C reduction method and by the luminol amplified chemiluminescence (CL) assay. RESULTS: Incubation with NS or HS increased Giardia adherence to PMNs from 6.9 +/- 3.2% (basal adherence of Giardia incubated in buffer) to 39 +/- 18.6% (p <0.01) and 76 +/- 19.5% (p <0.001), respectively. In absence of serum, Giardia failed to trigger an oxidative response of PMNs. Opsonization with NS or HS increased the PMN O2(-) production from 3.9 +/- 0.92 nmol/2.5 x 10(6) PMNs/10 min to 9.04 +/- 1.68 (p <0.05) and 17.9 +/- 1.32 (p <0.001), respectively. A similar enhancement of the CL response was also observed. The inactivation of complement activity by heat as well as the elimination of specific antibodies by absorption produced a significant abrogation of the oxidative response but in the case of HS heat inactivation alone did not abolish the response. Similar findings (variable abrogation of the oxidative PMN response) were observed when PMNs were incubated with monoclonal antibodies directed against complement C3, C3b or the low-affinity Fc receptors (CR1, CR3 or FcRlo). CONCLUSIONS: These results show that complement components and specific antibodies influence in the Giardia-PMN interaction. Although components of complement can contribute to the RB of PMNs, specific antibodies are critical for an optimal oxidative PMN response.