Unmethylated CpG dinucleotide motifs in bacterial DNA, as well as oligodeoxynucleotides (ODN) containing these motifs, are potent stimuli for many host immunological responses. These CpG motifs may enhance host responses to bacterial infection and are being examined as immune activators for therapeutic applications in cancer, allergy/asthma, and infectious diseases. However, little attention has been given to processes that down-modulate this response. The iron-binding protein lactoferrin is present at mucosal surfaces and at sites of infection. Since lactoferrin is known to bind DNA, we tested the hypothesis that lactoferrin will bind CpG-containing ODN and modulate their biological activity. Physiological concentrations of lactoferrin (regardless of iron content) rapidly bound CpG ODN. The related iron-binding protein transferrin lacked this capacity. ODN binding by lactoferrin did not require the presence of CpG motifs and was calcium independent. The process was inhibited by high salt, and the highly cationic N-terminal sequence of lactoferrin (lactoferricin B) was equivalent to lactoferrin in its ODN-binding ability, suggesting that ODN binding by lactoferrin occurs via charge-charge interaction. Heparin and bacterial LPS, known to bind to the lactoferricin component of lactoferrin, also inhibited ODN binding. Lactoferrin and lactoferricin B, but not transferrin, inhibited CpG ODN stimulation of CD86 expression in the human Ramos B cell line and decreased cellular uptake of ODN, a process required for CpG bioactivity. Lactoferrin binding of CpG-containing ODN may serve to modulate and terminate host response to these potent immunostimulatory molecules at mucosal surfaces and sites of bacterial infection.

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CD4+ Th cell infiltration into the brain and the activation by cellular elements of the central nervous system (CNS) are thought to be important steps in the initiation of CNS autoimmune diseases. T cell activation requires Ag-specific stimulation and additional costimulatory signals provided by the APC. Here we describe how murine brain microvessel endothelial (En) cells and smooth muscle/pericytes (SM/P) selectively induce the Ag-specific activation of different Th1 and Th2 CD4+ T cell clones. Th1 and Th2 cell clones were used that were specific for the same peptide Ag in the context of the same class II allotype. SM/P preferentially activated Th1 cell clones, whereas En cells activated Th2 cell clones better, as reflected by cell proliferation and production of IL-2 by SM/P-activated Th1 clones and IL-4 by Th2 clones. There was no difference in the level of expression of CD4, CD2, or LFA-1 molecules between these Th cell clones, and anti-CD4, CD2, LFA-1 or ICAM-1 mAb did not differentially affect Ag-induced proliferation among the clones. Moreover, antibody to CD28 did not influence Ag presentation by brain microvessel En or SM/P cells to Ag-specific Th1 and Th2 clones. These results suggest that: 1) different The subsets might require different signals for their activation; 2) different APC might provide different costimulatory signals for Th cell subsets; and 3) brain microvessel En and SM/P might play a differential role in induction of autoreactive T cell responses in the CNS.