Paul M. Guyre

Increased potency of Fc-receptor-targeted antigens

Abstract A major challenge for using native and modified T cell epitopes to induce or suppress immunity relates to achieving efficient uptake and processing by antigen-presenting cells (APC) in vivo. IgG Fc receptors, which are expressed constitutively by professional APC including monocytes and dendritic cells, have long been known to mediate antigen uptake in a manner leading to efficient T cell activation. We have previously demonstrated enhanced presentation of antigenic and antagonistic peptides by targeting them to the type I Fc receptor for IgG (FcγRI, CD64) on human monocytes. In the present report we review the literature suggesting that CD64-targeted antigens are likely to be effective in vivo, and present data demonstrating enhanced immunogenicity in CD64 transgenic mice of a fusion protein that combines the specificities of HIV gp120 and the humanized anti-CD64 monoclonal antibody H22. Overall, these studies suggest that targeting antigens to CD64 represents an effective approach to enhancing the effectiveness of vaccines in vivo.

Spontaneous aggregation as a mechanism for human monocyte purification

A previously unreported property of human mononuclear phagocytes is the ability of these cells to spontaneously aggregate. Fresh mononuclear cells obtained after plateletpheresis were noted to spontaneously form large cellular aggregates. Dual parameter immunofluorescence analysis demonstrated that the aggregating cells were positive for the monocyte marker CD11 (complement receptor, type 3) but were negative for the lymphocyte marker CD3 (T3 antigen). In addition, less than 5% of the nonaggregating cells were CD11+, suggesting that almost all CD11+ cells aggregated. Cellular aggregates were independent of cell concentration and formed more efficiently at 4 degrees C than at either 22 or 37 degrees C. Based on these observations, a purification procedure utilizing Ficoll-Hypaque separation, spontaneous aggregation at 4 degrees C, and transient plastic adherence resulted in a sevenfold enrichment of the CD11+ peripheral blood monocytes. Purified monocytes were contaminated with less than 2% CD3 cells. The size, growth, and adherence characteristics as well as cytologic stains indicated that the monocytes were not significantly altered by the purification procedure. Thus, spontaneous aggregation is an efficient and convenient method for the isolation of large numbers of purified monocytes.

Effect of morphine and β-endorphin on human Fc receptor-dependent and natural killer cell functions

Interactions between opiates and the human immune system have important clinical implications. To further evaluate these interactions, we studied in vitro and in vivo effects of morphine sulfate (morphine) and beta-endorphin (Bend) on antibody-dependent cell cytotoxicity (ADCC), natural killer cell cytotoxicity (NKCC), and effector cell expression of antibody Fc receptors. Morphine and Bend had no potent in vivo or in vitro effect on FcR expression nor did they have a significant in vitro effect on ADCC by monocytes or polymorphonuclear cells. Bend enhancement of NKCC in vitro was inhibited by coincubation of effector cells with morphine. After taking 90 to 150 mg of oral morphine, study volunteers demonstrated a significant decrease in ADCC by peripheral blood mononuclear cells. The same individuals demonstrated a consistent increase in NKCC and no change in the expression of Fc receptors. Effector cells from these individuals responded normally to in vitro incubation with interferon-gamma (IFN-gamma).

Uptake of Antigen-Antibody Complexes by Human Dendritic Cells

Fc receptors specific for IgG (FcγR) potentiate the immune response by facilitating the interaction between myeloid cells and antibody-coated targets (1-3). Monocyte and neutrophil FcyR engagement can lead to the induction of lytic-type mechanisms associated with innate responses. FcyR triggering can also play a key role in adaptive immune responses. For example, FcyR-directed capture and uptake of antigens (Ag) by dendritic cells (DC) results in processing and presentation to naive Ag-specific T cells, leading to their expansion and maturation into effector T-cell populations. This chapter describes methodology currently in use to explore and manipulate antigen-antibody (Ag-Ab) uptake by FcyR expressed on DC.