Lysolecithin analogs as adjuvants in delayed-type hypersensitivity in mice. I. Characterization of the adjuvant effect

Modified lipoproteins provide lipids that modulate dendritic cell immune function

Both physiological and pathological situations can result in biochemical changes of low-density lipoproteins (LDL). Because they can deliver signals to dendritic cells (DC), these modified lipoproteins now appear as regulators of the immune response. Among these modified lipoproteins, oxidized LDL (oxLDL) that accumulate during inflammatory conditions have been extensively studied. Numerous studies have shown that oxLDL induce the maturation of DC, enhancing their ability to activate IFNγ secretion by T cells. LDL treated by secreted phospholipase A(2) also promote DC maturation. Among the bioactive lipids generated by oxidation or phospholipase treatment of LDL, lysophosphatidylcholine (LPC) and some saturated fatty acids induce DC maturation whereas some unsaturated fatty acids or oxidized derivatives have opposite effects. Among other factors, the nuclear receptor peroxisome-proliferator activated receptor γ (PPARγ) plays a crucial role in this regulation. Non-modified lipoproteins also contribute to the regulation of DC function, suggesting that the balance between native and modified lipoproteins, as well as the biochemical nature of the LDL modifications, can regulate the activation threshold of DC. Here we discuss two pathological situations in which the impact of LDL modifications on inflammation and immunity could play an important role. During atherosclerosis, modified LDL accumulating in the arterial intima may interfere with DC maturation and function, promoting a Th1 immune response and a local inflammation favoring the development of the pathology. In patients chronically infected, the hepatitis C virus (HCV) interferes with lipoprotein metabolism resulting in the production of infectious modified lipoproteins. These lipo-viral-particles (LVP) are modified low-density lipoproteins containing viral material that can alter DC maturation and affect specific toll-like receptor signaling. In conclusion, lipoprotein modifications play an important role in the regulation of immunity by delivering signals of danger to DC and modulating their function.

Sensitivity of human hematopoietic cell lines to an alkyl-lysophospholipid-derivative

A panel of 16 human hematopoietic cell lines was tested for sensitivity to racemic 1-0-octadecyl-2-0-methyl-glycero-3-phosphocholine (ALP). Effects on proliferation rate, cell cycle distribution, viability and morphology were examined. Cell growth was heavily retarded for all lines at an ALP concentration of 10 micrograms ml-1, which induced profound cell death. 1 microgram ml-1 of ALP was a suitable concentration to make comparisons between the different cell lines. In sensitive lines cell growth was retarded due to induction of multinucleated cells and cytotoxicity. The multinucleated cells could proceed through the cell cycle but cell division was inhibited. The most ALP sensitive cell lines (MN-60, P3Hr-1, Um-42 and RPMI 8226) were B-cell lines, whereas the most resistant lines (U-61M, K562-4 and CCRF-CEM) were of different cell origin. In conclusion, a variable response to ALP was found in 16 human hematopoietic cell lines. As a rule sensitivity to ALP was demonstrated as increased cell death and induction of cells with less than or equal to 2 nuclei, leading to a decreased cell number as compared to control cells.

Stereospecific chemoattraction of lymphoblastic cells by gradients of lysophosphatidylcholine

Human plasma contains chemoattractant activity for cultured cells from the mouse thymic lymphoma 6C3HED and also for lymphoblasts from concanavalin A-stimulated mouse spleen cells. A major portion of the attractant activity for both cell types could be attributed to plasma lysophosphatidylcholine. Studies on synthetic lysophosphatides showed that polar head group structure, acyl chain length, and stereochemical configuration are important determinants for attractant activity.

Antigenic, adjuvant and permeability enhancing properties of melittin in mice

Melittin, a mast cell lytic agent which comprises 50% of the protein content of bee venom, may be responsible for some of the severe reactions produced by bee stings in allergic and non-allergic individuals. We therefore investigated some of the biologic properties of this molecule in mice and found that repeated intradermal injections of melittin without adjuvant induced IgE formation in mice. In addition, melittin as well as another surfactant, saponin, were potent adjuvants for IgE formation in mice when mixed with ovalbumin (Ov). Titres of 1280 and 2560 to ovalbumin were produced in CBA mice after two injections of melittin and Ov or saponin and Ov. Melittin was also shown to have an enhancing effect on the vascular permeability induced by an antigen antibody interaction in mouse skin. Evan's blue dye was injected intravenously into ovalbumin-sensitized mice which had been injected intradermally with ovalbumin alone, melittin alone or a mixture of melittin and ovalbumin. The amount of local extravasation of dye was significantly greater in the area injected with the melittin and ovalbumin mixture than the amount of dye obtained from the skin site injected with melittin alone plus that extracted from the site injected with ovalbumin alone.

Lysolecithin analogs as adjuvants in delayed-type hypersensitivity in mice. II. Studies on the mode of action

Lysolecithin analogs (LLA) possess adjuvant activity in delayed-type hypersensitivity (DTH). To elucidate their mode of action, we studied the influence of LLA on the recruitment of hemopoietic progenitor cells and on the induction and transfer of DTH. Whereas the number and composition of colony-forming cells (CFC) in the bone marrow remained unaltered in LLA-treated mice, the number of CFC in the spleen was augmented severalfold, and the content of macrophage progenitors was remarkably increased. DTH was induced with macrophages from peritoneal cells (PC) pulsed with keyhole limpet hemocyanin (KLH). A more marked DTH response was obtained with KLH-pulsed PC from LLA-treated mice than from mice given phosphate-buffered saline (PBS). On the other hand, there was no difference in the DTH response following adoptive transfer of sensitized cells to naive mice pretreated either with PBS or LLA. It is concluded that the adjuvant effect of LLA can be accounted for partly in terms of their effects on macrophage progenitors and partly in terms of a more effective T cell activation by antigens associated with LLA-derived macrophages.