Cross talk among bacteria and dendritic cells

Dentric cells (DC) play a crucial role in the immune system as they are the professional antigen-presenting cells (APC) most efficient in the activation of resting T lymphocytes and thus initiate primary immune responses. This activity is believed to be crucially controlled by micro environmental signals. DC have a privileged distribution in tissues interfacing the external environment thus acting as efficient sentinels for recognition of invading microorganism. Consistent with this hypothesis, we have shown that DC can internalize bacteria into phagosomes and that both gram-positive and gram-negative bacteria functions as DC activators. The ability of DC phagocytose particulates or bacteria is more pronounced immature, less-differentiated cells than in mature DC, this capacity being downregulated upon activation. Activation of DC by bacteria can be shown phenotypicall. Incubation of DCs with different including Streptococcus pneumoniae, Streptococcus phyogenes, Streptococcus gordonii, Staphylococcus aureus, Lactococcus lactis, Lactobacillus acidophilus, Mycobacterium smegmatis, Salmonella Ty2la, Escherichia coli, Mycobacterium etc., resulted in modification of surface activation markers. Consistent with acquisition of costimulating activity is the upregulation of both B7.2 (CD86) and CD40. The binding of B7.2 with its ligand on T cells (CD28 or CTLA-4) results in a costimulatory signal for cytokine production and T cell proliferation. Functional DC activation was followed using well characterized T cell hybridomas specific for peptides of ovalbumin (OVA) and a recombinant strain of Streptococcus gordonii engineered to express OVA.