Triggering DTH and CTL activity by fd filamentous bacteriophages: role of CD4+ T cells in memory responses

Abstract

The ability of fd bacteriophage particles to trigger different arms of the immune system has been previously shown by us with particular emphasis on the ability of phages to raise CTL responses in vitro and in vivo. Here we show that fd virions in the absence of adjuvants are able to evoke a DTH reaction mediated by antigen specific CD8+ T cells. In addition, we analyzed the induction of CTL responses in mice depleted of CD4+ T cells, and we observed that short-term secondary CTL responses were induced in the absence of CD4+ T cells while induction of long-term memory CTLs required the presence of CD4+ T lymphocytes. These results examine the cellular mechanism at the basis of fd efficiency and provide new elements to further validate the use of fd particles for eliciting and monitoring antigen-specific CTLs.

Figure 1

fdOVA_257–264 administration is able to trigger DTH. Mice were sensitized by one injection of 50 μg of cytotoxic OVA_257–264 (SIINFEKL) peptide and 140 μg T helper HBVc_128–140 (TPPAYRPPNAPIL) peptide from hepatitis B virus core antigen, emulsified with incomplete Freund's adjuvant. Ten days after sensitization, DTH was performed by injecting into the right footpad fdOVA_257–264, fdwt, the synthetic OVA_257–264 peptide (pepOVA), or soluble ovalbumin. 10–48 hours later the area of swelling was measured using a caliper. (a) Curve response of all mice analyzed. (b) Values at 30 hours of mean thickness ± SD of the different mice groups challenged with the antigens indicated in the abscissa. The P-values were calculated by comparing each group with the fdOVA_257–264 challenged group.

Figure 2

CTL and IFN-γ responses in mice immunized with fd bacteriophage particles in the presence or in the absence of CD4+ T cell help. Mice were immunized by two injections with either fdOVA_257–264 plus poly I:C or fdOVA_257–264 particles as indicated in Materials and Methods. Immunizations with fdOVA_257–264 particles were also performed in mice depleted of CD4+ T cells by treatment with GK1.5 mAb. CTL and IFN-γ productions were assayed after 15 days (a, b) or after two months (c, d) from the last injection. Each symbol represents data obtained from a single mouse. The mean value ± SD for each group is reported. (e) CD4+ T cell depletion was analyzed by cytofluorometry using noncompeting anti-CD4 antibody. The analysis was performed on spleen cells isolated from mice sacrificed at the time points indicated.