Neutrophils play a crucial early role during the innate response, but little is known about their possible contribution when an adaptive immune response is installed. A robust neutrophilia and a T helper 1 (Th1) immune response are present after immunization with Complete Freund Adjuvant (CFA). We show that when FITC-labeled OVA was injected into the footpad of OVA/CFA immunized mice, the main OVA-FITC+ cells recruited in draining popliteal lymph nodes (LNs) were neutrophils, with most of them arriving at the LN by means of lymphatic vessels. The development of this OVA-FITC+ neutrophil influx requires an immune response against OVA. The OVA-FITC+ neutrophils present in LNs displayed mainly intracellular TNF-alpha, and their depletion resulted in an increase in the specific IL-5 levels. These data provide new evidence about the role played by neutrophils in vivo in adaptive immunity.

Synopsis The parasite Giardia lamblia possesses peripheral vacuoles (PVs) that function as both endosomes and lysosomes and are implicated in the adaptation, differentiation, and survival of the parasite in different environments. The mechanisms by which Giardia traffics essential proteins to these organelles and regulates their secretion have important implications in the control of parasite dissemination. In this study, we describe the participation of the heterotetrameric clathrin-adaptor protein gAP2 complex in lysosomal protein trafficking. A specific monoclonal antibody against the medium subunit (gμ2) of gAP2 showed localization of this complex to the PVs, cytoplasm, and plasma membrane in the growing trophozoites. gAP2 also colocalized with clathrin in the PVs, suggesting its involvement in endocytosis. Uptake experiments using standard molecules for the study of endocytosis revealed that gAP2 specifically participated in the endocytosis of LDL. Targeted downregulation of the gene encoding gμ2 in growing and encysting trophozoites resulted in a large decrease in the amount of cell growth and cyst wall formation, suggesting a distinct mechanism in which gAP2 is directly involved in both endocytosis and vesicular trafficking.

The protozoan parasite Giardia lamblia uses arginine deiminase (ADI) to produce energy from free L-arginine under anaerobic conditions. In this work, we demonstrate that, in addition to its known role as a metabolic enzyme, it also functions as a peptidylarginine deiminase, converting protein-bound arginine into citrulline. G. lamblia ADI specifically binds to and citrullinates the arginine in the conserved CRGKA tail of variant-specific surface proteins (VSPs), affecting both antigenic switching and antibody-mediated cell death. During encystation, ADI translocates from the cytoplasm to the nuclei and appears to play a regulatory role in the expression of encystation-specific genes. ADI is also sumoylated, which might modulate its activity. Our findings reveal a dual role played by ADI and define novel regulatory pathways used by Giardia for survival.