Abstract
Liposomes containing phosphatidylcholine have been widely used as adjuvants. Recently, we demonstrated that B-1 cells produce dipalmitoyl-phosphatidylcholine (DPPC)-specific IgM upon immunization of BALB/c mice with DPPC-liposomes encapsulating ovalbumin (OVA). Although this preparation enhanced the OVA-specific humoral response, the contribution of anti-DPPC antibodies to this effect was unclear. Here, we demonstrate that these antibodies are secreted by B-1 cells independently of the presence of OVA in the formulation. We also confirm that these antibodies are specific for phosphocholine. The anti-OVA humoral response was partially restored in B-1 cells-deficient BALB/xid mice by immunization with the liposomes opsonized with the serum total immunoglobulin (Ig) fraction containing anti-phosphocholine antibodies, generated in wild-type animals. This result could be related to the increased phagocytosis by peritoneal macrophages of the particles opsonized with the serum total Ig or IgM fractions, both containing anti-phosphocholine antibodies. In conclusion, in the present work, it has been demonstrated that phosphocholine-specific antibodies improve T-dependent antibody responses against OVA carried by DPPC-liposomes.
Highlights
IgM is the first antibody isotype to appear during ontogeny and the only isotype produced by all species of vertebrates [1, 2]
To characterize the immune response induced by liposomal lipid DPPC, BALB/c mice were immunized with Lp DPPC with or without encapsulated OVA
Liposomal DPPC induced a primary antibody response that was significantly impaired in B-1 cells-deficient BALB/xid mice (Figure 1C), indicating the crucial role of this B cell population, as had been demonstrated for Lp DPPC-containing
Summary
IgM is the first antibody isotype to appear during ontogeny and the only isotype produced by all species of vertebrates [1, 2] It is the first isotype produced during an immune response and plays a crucial role in front-line host defense against pathogens. There is a distinct set of natural antibodies that bind to determinants that arise on erythrocytes during their senescence or after enzymatic treatment with bromelain [10, 17,18,19] These anti-red cell antibodies are reported to recognize determinants that involve the entire phosphatidylcholine molecule in the outer cell membrane, but not other phosphocholine-containing antigens
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