T Helper Cells Play a Critical Role in the Humoral Response to Hapten Carrier Conjugates

As Chapter 3 described, when animals are immunized with small organic compounds (haptens) conjugated with large proteins (carriers), the conjugate induces a humoral immune response consisting of antibodies both to hapten epitopes and to unaltered epitopes on the carrier protein. Hapten-carrier conjugates provided immunologists with an ideal system for studying cellular interactions of the humoral response, and such studies demonstrated that the generation |of a humoral antibody response requires recognition of the antigen by both TH cells and B cells, each recognizing different epitopes on the same antigen. A variety of different hapten-carrier conjugates have been used in immunologic research (Table 11-5).

One of the earliest findings with hapten-carrier conjugates was that a hapten had to be chemically coupled to a larger carrier molecule to induce a humoral response to the hapten. If an animal was immunized with both hapten and carrier separately, very little or no hapten-specific antibody was generated. A second important observation was that, in order to generate a secondary antibody response to a hapten,

TABLE 11-5

Common hapten-carrier conjugates used in immunologic research

Hapten-carrier

TABLE 11-5

Hapten-carrier

acronym

Hapten

Carrier protein

DNP-BGG

Dinitrophenol

Bovine gamma globulin

TNP-BSA

Trinitrophenyl

Bovine serum albumin

NIP-KLH

5-Nitrophenyl acetic acid

Keyhole limpet hemocyanin

ARS-OVA

Azophenylarsonate

Ovalbumin

LAC-HGG

Phenyllactoside

Human gamma globulin

X-irradiated syngeneic mouse

Secondary anti-DNP

response:

X-irradiated syngeneic mouse

1° BGG Spleen cells

+ X-irradiated syngeneic mouse

Anti-Thy-1

complement

1° BGG Spleen cells

+ X-irradiated syngeneic mouse

Anti-Thy-1

complement

1° DNP-BSA Spleen cells

complement

1° DNP-BSA Spleen cells

Dnp Bsa Mouse

X-irradiated syngeneic mouse

FIGURE 11-15

X-irradiated syngeneic mouse

FIGURE 11-15

Cell-transfer experiments demonstrating that hapten-primed and carrier-primed cells are separate populations.

(a) X-irradiated syngeneic mice reconstituted with spleen cells from both DNP-BSA-primed mice and BGG-primed mice and challenged with DNP-BGG generated a secondary anti-DNP response.

(b) Removal of T cells from the BGG-primed spleen cells, by treatment with anti-Thy-1 antiserum, abolished the secondary anti-DNP response. (c) Removal of T cells from the DNP-BSA-primed spleen cells had no effect on the secondary response to DNP. These experiments show that carrier-primed cells are T cells and hapten-primed cells are B cells.

the animal had to be again immunized with the same hapten-carrier conjugate used for the primary immunization. If the secondary immunization was with the same hapten but conjugated to a different, unrelated carrier, no secondary anti-hapten response occurred. This phenomenon, called the carrier effect, could be circumvented by priming the animal separately with the unrelated carrier.

Similar experiments conducted with a cell-transfer system showed that cells immunized against the hapten and cells immunized against the carrier were distinct populations. In these studies, one mouse was primed with the DNP-BSA conjugate and another was primed with the unrelated carrier BGG, which was not conjugated to the hapten. In one experiment, spleen cells from both mice were mixed and injected into a lethally irradiated syngeneic recipient. When this mouse was challenged with DNP conjugated to the unrelated carrier BGG, there was a secondary anti-hapten response to DNP (Figure 11-15a). In a second experiment, spleen cells from the BGG-immunized mice were treated with anti-T-cell antiserum (anti-Thy-1) and complement to lyse the T cells. When this T-cell-depleted sample was mixed with the DNP-BSA-primed spleen cells and injected into an irradiated mouse, no secondary anti-hapten response was observed upon immunizing with DNP-BGG (Figure 11-15b). However, similar treatment of the DNP-BSA-primed spleen cells with anti-Thy-1 and complement did not abolish the secondary anti-hapten response to DNP-BGG (Figure 11-15c). Later experiments, in which antisera were used to specifically deplete CD4+ or CD8+ T cells, showed that the CD4+ T-cell subpopulation was responsible for the carrier effect. These experiments demonstrate that the response of hapten-primed B cells to the hapten-carrier conjugate requires the presence of carrier-primed CD4+ TH cells specific for carrier epitopes. (It is important to keep in mind that the B-cell response is not limited to the hapten determinant; in fact some B cells do react to epitopes on the carrier; however, the assay can be conducted in such a manner as to detect only anti-hapten responses.)

The experiments with hapten-carrier conjugates revealed that both Th cells and B cells must recognize antigenic determinants on the same molecule for B-cell activation to occur. This feature of the T- and B-cell interaction in the humoral response is called associative, or linked, recognition. The conclusions drawn from hapten-carrier experiments apply to the humoral response to antigens in general and support the requirement for T-cell help in B-cell activation described earlier in this chapter.

Was this article helpful?

0 0
Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

Get My Free Ebook


Responses

  • Ren
    What is a x irradiated syngeneic mouse?
    8 years ago

Post a comment