Antigen targeting to dendritic cells elicits long-lived T cell help for antibody responses

Abstract

Resistance to several prevalent infectious diseases requires both cellular and humoral immune responses. T cell immunity is initiated by mature dendritic cells (DCs) in lymphoid organs, whereas humoral responses to most antigens require further collaboration between primed, antigen-specific helper T cells and naive or memory B cells. To determine whether antigens delivered to DCs in lymphoid organs induce T cell help for antibody responses, we targeted a carrier protein, ovalbumin (OVA), to DCs in the presence of a maturation stimulus and assayed for antibodies to a hapten, (4-hydroxy-3-nitrophenyl) acetyl (NP), after boosting with OVA-NP. A single DC-targeted immunization elicited long-lived T cell helper responses to the carrier protein, leading to large numbers of antibody-secreting cells and high titers of high-affinity antihapten immunoglobulin Gs. Small doses of DC-targeted OVA induced higher titers and a broader spectrum of anti-NP antibody isotypes than large doses of OVA in alum adjuvant. Similar results were obtained when the circumsporozoite protein of Plasmodium yoelii was delivered to DCs. We conclude that antigen targeting to DCs combined with a maturation stimulus produces broad-based and long-lived T cell help for humoral immune responses.

Figure 1.

Immunization with anti–DEC-OVA fusion mAb primes OVA-specific T cells. IFN-γ production by CD4⁺ and CD8⁺ T cells is shown as dot plots of gated CD3⁺ T cells stained for CD4 and intracellular IFN-γ. Immunization conditions are displayed on the right, and the peptide pool numbers are shown on top. Numbers represent the percent of IFN-γ⁺ CD3⁺ CD4⁻ (left panels) or IFN-γ⁺ CD3⁺ CD4⁺ (right panels) T cells.

Figure 2.

Immunization with anti–DEC-OVA fusion mAb primes helper T cells for antibody responses. (A) Anti-NP IgG antibody titers before and 7 or 14 d after an i.p. boost injection with 1 μg OVA-NP₁₁ in PBS. Immunization conditions are displayed at the top. Symbols represent individual mice, and the curves represent the mean value of each group. (B) Antibody-secreting cells in the spleen or bone marrow measured by ELISPOT on NP₂-BSA 14 d after an i.p. boost with 1 μg OVA-NP₁₁ in PBS. Symbols indicate individual mice. Initial immunization conditions were as follows: PBS (▪), anti–DEC-OVA (▴), anti–DEC-OVA plus anti-CD40 plus poly I:C (▾), control-OVA plus anti-CD40 plus poly I:C (♦), anti-CD40 plus poly I:C (•), and alum plus OVA (×). (C) Anti-NP antibody titers for individual IgG isotypes and IgM 14 d after an i.p. boost with 1 μg OVA-NP₁₁ in PBS. The horizontal lines represent the mean value of each group. Symbols indicate individual mice and initial immunization conditions as described in B. (D) Anti-NP IgG antibody responses measured by ELISA in mice immunized with anti–DEC-OVA plus anti-CD40 plus poly I:C 4, 6, 8, or 12 wk before i.p. boosting with 1 μg OVA-NP₁₁ in PBS. Antibody titers were measured as described in A. (E) Anti-OVA IgG antibody titers in mice immunized with anti–DEC-OVA plus anti-CD40 plus poly I:C and then boosted 6 wk later with 1 μg of either OVA, anti–DEC-OVA, or control-OVA. Antibody titers were measured as described in A.

Figure 3.

Immunization with αDEC-CS primes helper and CD8⁺ T cells. (A) IFN-γ production by CD4⁺ (A) and CD8⁺ (B) T cells measured by ELISPOT assay 14 d after immunization. Plots show numbers of spots per 10⁶ T cells from mice immunized i.p. with 10 μg αDEC-CS plus anti-CD40 plus poly I:C (black bars) or PBS (striped bars), or anti-CD40 plus poly I:C (gray bars) or i.v. with 7.5 × 10⁴ irradiated sporozoites (white bars). Mouse strains are indicated at the top.

Figure 4.

Immunization with DEC-CS primes helper cells for antibody responses. (A) Anti-QGPGAP IgG antibody titers before and 7 d after an i.p. boost injection with 10 μg αDEC-CS in PBS. Immunization conditions are displayed at the top of each panel. Symbols represent individual mice, and the curves represent the mean value of each group. (B) Anti-QGPGAP antibody titers for individual IgG isotypes and IgM 7 d after an i.p. boost with 10 μg αDEC-CS in PBS. The horizontal lines represent the mean value of each group. Initial immunization conditions were as follows: PBS (▪), αDEC-CS plus anti-CD40 plus poly I:C (▾), and anti-CD40 plus poly I:C (•). As control, one group of mice was immunized with 7.5 × 10⁴ irradiated sporozoites (×) and bled 8 wk later at the same time as the other groups. Symbols represent individual mice.