Naive T-cell receptor transgenic T cells help memory B cells produce antibody

Abstract

Injection of the same antigen following primary immunization induces a classic secondary response characterized by a large quantity of high-affinity antibody of an immunoglobulin G class produced more rapidly than in the initial response - the products of memory B cells are qualitatively distinct from that of the original naive B lymphocytes. Very little is known of the help provided by the CD4 T cells that stimulate memory B cells. Using antigen-specific T-cell receptor transgenic CD4 T cells (DO11.10) as a source of help, we found that naive transgenic T cells stimulated memory B cells almost as well (in terms of quantity and speed) as transgenic T cells that had been recently primed. There was a direct correlation between serum antibody levels and the number of naive transgenic T cells transferred. Using T cells from transgenic interleukin-2-deficient mice we showed that interleukin-2 was not required for a secondary response, although it was necessary for a primary response. The results suggested that the signals delivered by CD4 T cells and required by memory B cells for their activation were common to both antigen-primed and naive CD4 T cells.

Figure 1

Model to evaluate the ability of transgenic KJ⁺ CD4⁺ T cells to provide help for memory B cells. (a) Naive KJ⁺ CD4⁺ T cells help primed B cells but not naive B cells following sol-OVA challenge. SCID recipients were injected with 3 × 10⁵ naive KJ⁺ CD4⁺ T cells together with 10⁷ primed B cells or 10⁷ naive B cells or with 10⁷ primed B cells alone as a control. Mice were challenged i.p. with 10 μg sol-OVA immediately after transfer and anti-OVA antibody levels were measured on day 14. The values represent the geometric means + SD of six recipients per group. (b) The effect of antigen dose on antibody production by primed B cells. SCID recipients received 10⁷ primed B cells alone (con), or together with 3 × 10⁵ naive KJ⁺ CD4⁺ T cells, and were challenged i.p. with 10 μg or 100 μg sol-OVA. The values shown represent the geometric means + SD of five or two (control) recipients per group. (c) Titration of primed B cells. SCID recipients were injected with 3 × 10⁶, 10⁷ or 3 × 10⁷ primed B cells together with 3 × 10⁶ KJ⁺ CD4⁺ T cells; mice were challenged i.p. with 10 μg sol-OVA immediately after transfer and bled 14 days later. The values represent the geometric means + SD of six recipients per group.

Figure 2

Comparison of help provided by naive and primed KJ⁺ CD4⁺ T cells for primed B cells. (a) A representative analysis of naive KJ⁺ CD4⁺ T cells from DO11.10-SCID donors expressing a CD45RB^hi phenotype. (b) An analysis of primed KJ⁺ CD4⁺ T cells used for injection recovered from intermediate SCID mice injected 10 days earlier with 100 μg ap-OVA-pep and depleted of CD45RB^hi T cells. SCID recipients were injected with 3 × 10⁵ (c) or 1 × 10⁵ (d) naive or primed KJ⁺ CD4⁺ T cells together with 10⁷ primed B cells, challenged immediately with 10 μg sol-OVA, and antibody levels measured on selected days. Control groups received 10⁷ B cells alone. Values represent the geometric means + SD of six recipients per group (naive vs primed, *P < 0·05).

Figure 3

The response by primed B cells is limited by the number of transgenic T cells transferred. SCID recipients were injected with 10⁷ primed B cells together with graded doses of KJ⁺ CD4⁺ T cells, challenged i.p. with 10 μg sol-OVA immediately after cell transfer and serum was collected on day 14. The values represent the geometric means + SD of four to six recipients per group.

Figure 4

Transgenic T cells from DO11.10-IL-2^–/– mice help memory but not naive B cells produce antibody. (a) Primary response: SCID mice received 10⁷ naive B cells from non-immunized mice together with 3 × 10⁵ T cells from naive DO11.10-IL-2^–/– mice (IL-2 KO), or from naive conventional DO11.10 mice (KJ) or received no transgenic T cells. All recipients were challenged with 100 μg ap-OVA on the day of transfer. Values represent the geometric means + SD of six recipients per group (IL-2 KO versus KJ: *P < 0·05; ***P < 0·001). (b) Secondary response: SCID mice were injected with 10⁷ B cells from OVA-primed mice together with 3 × 10⁵ naive transgenic T cells from DO11.10-IL-2^–/– (IL-2 KO), or DO11.10 donors (KJ), or 3 × 10⁵ T cells from DO11.10-IL-2^–/– mice plus twice daily injections of 3 × 10⁵ IU rIL-2 per day for 6 days (IL-2 KO + IL-2), or no T cells (pr B cells only). All recipients were challenged with 10 μg sol-OVA on the day of transfer. Values represent the geometric means + SD of six recipients per group.