Memory T cells enhance the expression of high-avidity naive B cells

Vaccination to gain humoral immune memory

The concept of immune memory forms the biological basis for vaccination programs. Despite advancements in the field of immune memory and vaccination, most current vaccines are evaluated by magnitude of antigen-specific antibody titers in serum or mucosa after vaccination. It has been shown, however, that antibody-mediated humoral immune memory is established regardless of the magnitude and duration of immune reactions, suggesting that assessment of vaccine efficacy should be performed for several years after vaccination. This long-term investigation is disadvantageous for prevalent and pandemic infections. Long-lived memory plasma cells and memory helper T cells which contribute to humoral immune memory are generated in the bone marrow after migration of memory cell precursors through bloodstream. Thus, it may be a novel evaluation strategy to assess the precursors of memory cells in the blood in the early phase of the immune reaction(s). We here review recent advances on the generation and maintenance of immune memory cells involved in humoral immunity and introduce a current concept of direct and short-term assessment of humoral immune memory formation upon vaccination as a correlate of protection.

Thy1+IL-7+ lymphatic endothelial cells in iBALT provide a survival niche for memory T-helper cells in allergic airway inflammation

Memory CD4(+) T helper (Th) cells are central to long-term protection against pathogens, but they can also be pathogenic and drive chronic inflammatory disorders. How these pathogenic memory Th cells are maintained, particularly at sites of local inflammation, remains unclear. We found that ectopic lymphoid-like structures called inducible bronchus-associated lymphoid tissue (iBALT) are formed during chronic allergic inflammation in the lung, and that memory-type pathogenic Th2 (Tpath2) cells capable of driving allergic inflammation are maintained within the iBALT structures. The maintenance of memory Th2 cells within iBALT is supported by Thy1(+)IL-7-producing lymphatic endothelial cells (LECs). The Thy1(+)IL-7-producing LECs express IL-33 and T-cell-attracting chemokines CCL21 and CCL19. Moreover, ectopic lymphoid structures consisting of memory CD4(+) T cells and IL-7(+)IL-33(+) LECs were found in nasal polyps of patients with eosinophilic chronic rhinosinusitis. Thus, Thy1(+)IL-7-producing LECs control chronic allergic airway inflammation by providing a survival niche for memory-type Tpath2 cells.

B Cells Negatively Regulate the Establishment of CD49b(+)T-bet(+) Resting Memory T Helper Cells in the Bone Marrow

During an immune reaction, some antigen-experienced CD4 T cells relocate from secondary lymphoid organs (SLOs) to the bone marrow (BM) in a CD49b-dependent manner and reside and rest there as professional memory CD4 T cells. However, it remains unclear how the precursors of BM memory CD4 T cells are generated in the SLOs. While several studies have so far shown that B cell depletion reduces the persistence of memory CD4 T cells in the spleen, we here show that B cell depletion enhances the establishment of memory CD4 T cells in the BM and that B cell transfer conversely suppresses it. Interestingly, the number of antigen-experienced CD4 T cells in the BM synchronizes the number of CD49b⁺T-bet⁺ antigen-experienced CD4 T cells in the spleen. CD49b⁺T-bet⁺ antigen-experienced CD4 T cells preferentially localize in the red pulp area of the spleen and the BM in a T-bet-independent manner. We suggest that B cells negatively control the generation of CD49b⁺T-bet⁺ precursors of resting memory CD4 T cells in the spleen and may play a role in bifurcation of activated effector and resting memory CD4 T cell lineages.

Distinct energy requirements for human memory CD4 T-cell homeostatic functions

Differentiation and activation of CD4 memory T cells (T(mem) cells) require energy from different sources, but little is known about energy sources for maintenance and surveillance activities of unactivated T(mem) cells. Mitochondrial fatty acid oxidation (FAO) in human unactivated CD4 T(mem) cells was significantly enhanced by inhibition of glycolysis, with respective means of 1.7- and 4.5-fold for subjects <45 yr and >65 yr, and by stimulation of AMP-activated protein kinase, with respective means of 1.3- and 5.2-fold. However, CCL19 and sphingosine 1-phosphate (S1P), which control homeostatic lymphoid trafficking of unactivated T(mem) cells, altered FAO and glycolysis only minimally or not at all. Inhibition of CD4 T(mem)-cell basal FAO, but not basal glycolysis, significantly suppressed CCL19- and S1P-mediated adherence to collagen by >50 and 20%, respectively, and chemotaxis by >20 and 50%. Apoptosis of unactivated T(mem) cells induced by IL-2 deprivation or CCL19 was increased significantly by >150 and 70%, respectively, with inhibition of FAO and by >110 and 30% with inhibition of glycolysis. Anti-TCR antibody activation of T(mem) cells increased their chemotaxis to CCL5, which was dependent predominantly on glycolysis rather than FAO. The sources supplying energy for diverse functions of unactivated T(mem) cells differ from that required for function after immune activation.

Type II membrane protein CD69 regulates the formation of resting T-helper memory

Memory T-helper (Th) lymphocytes are crucial for the maintenance of acquired immunity to eliminate infectious pathogens. We have previously demonstrated that most memory Th lymphocytes reside and rest on stromal niches of the bone marrow (BM). Little is known, however, regarding the molecular basis for the generation and maintenance of BM memory Th lymphocytes. Here we show that CD69-deficient effector CD4 T lymphocytes fail to relocate into and persist in the BM and therefore to differentiate into memory cells. Consequently, CD69-deficient CD4 T cells fail to facilitate the production of high-affinity antibodies and the generation of BM long-lived plasma cells in the late phase of immune responses. Thus, CD69 is critical for the generation and maintenance of professional memory Th lymphocytes, which can efficiently help humoral immunity in the late phase. The deficit of immunological memory in CD69-deficient mice also highlights the essential role of BM for the establishment of Th memory.

Serum antibody levels and avidities to Escherichia coli O antigens and poliovirus type 1 antigen are increased in children treated for malignant disease

BACKGROUND

Treatment of malignant disease in children is often associated with low serum immunoglobulin and reduced specific antibody levels. The aim of this study was to investigate if the functional affinity of specific antibodies in serum and saliva is reduced as well and to evaluate if antigenic exposure or treatment duration affects this antibody avidity.

PROCEDURE

Serum samples were obtained from 45 children and salivary specimens from 30 children with malignant disease. The children were tested either prior to, during, or after chemotherapy. Levels of antibody to E. coli O and to poliovirus type 1 antigens were determined using an ELISA and isotype-specific relative antibody avidity was measured using thiocyanate to elute antibodies from solid-phase immobilized antigens.

RESULTS

Children with malignant disease had higher levels and relative avidity indexes of serum antibodies to both antigens as compared to controls. The duration of treatment and type of malignant disease were unrelated to these parameters. In saliva, the level of antibodies to E. coli O antigens, but not to poliovirus type 1 antigen, increased during treatment.

CONCLUSIONS

Both the amount and avidity of serum antibodies to these antigens are increased in children with malignant disease. This may be due to a dysregulation of the immune system caused by the malignancy and seems not to be dependent on exposure. In contrast, the avidity and levels of these antibodies in saliva seem to correlate with the presence of antigenic exposure.

Varicella-zoster virus antibody avidity and IgG-subclass patterns in children with recurrent chickenpox

The normal immune response after primary varicella-zoster virus (VZV) infection includes IgG subclass evolution to predominantly IgG1-type antibodies, and maturation from low to high avidity antibodies which are maintained for life. Twenty-three healthy and apparently immunocompetent children with a history of 2-5 episodes of chickenpox were studied after repeat disease. Serial sera were tested for VZV-IgG subclass patterns and VZV IgG and G-subclass antibody avidity by urea elution enzyme linked immunoassay (ELISA). Of 11 patients studied within 8 weeks of repeat chickenpox (Early Group), mean antibody avidity was significantly lower (31.3 +/- 26.81) than control (65.1 +/- 12.38) (P < .001). Seven had low avidity antibody (< 30 percent) and an abundance of IgG3 which was a pattern like primary chickenpox, and 2/11 had high avidity antibody characteristic of anamnestic responses. Early Group patients and 12 others studied over 8 weeks after repeat disease (Late Group) showed avidity maturation and attrition of IgG subclass antibodies other than IgG1. At least nine children failed to show VZV-specific secondary (memory) immune responses early in the course of repeat disease. It is possible that failure to maintain or evoke a secondary immune response could explain their susceptibility to repeat chickenpox.

Research note: avidity of chicken yolk antibodies to enterotoxigenic Escherichia coli fimbriae

The yolk antibodies from chickens and the serum and colostrum antibodies from cows were obtained after immunization of these animals with inactivated bacterin or purified K99 fimbriae from enterotoxigenic Escherichia coli (ETEC). The avidity of anti-K99 fimbriae antibodies produced from either chickens or cows was measured by competitive binding assay of ELISA. The yolk antibodies competed strongly with the serum and colostrum antibodies from immunized cows and inhibited 40 to 80% of the binding of these antibodies. Results demonstrate that the avidity of antibodies obtained from immunized chickens compares with that obtained from immunized cows. Thus, the yolk antibody from immunized chickens, aside from its use for prophylaxis against some infectious diseases, may also serve as effective ligand for purification of biologically active substances such as fimbrial antigens by affinity chromatographic procedures.

The influence of orientation and number of copies of T and B cell epitopes on the specificity and affinity of antibodies induced by chimeric peptides

CBA and TO mice were immunized with chimeric peptide immunogens consisting of B cell (residues 404-414) and T cell (residues 288-302) epitopes from the F protein of measles virus. The chimeras were co-linearly synthesized to contain one or two copies of the T cell epitope linked to one or two copies of the B cell epitope via a glycine.glycine spacer. Two orientations were synthesized such that the T cell epitope(s) were located at either the amino or carboxyl terminus of the B cell epitope(s). The levels of antibody induced following immunization with the chimeras were assessed by enzyme-linked immunosorbent assay using microtiter plates coated with either the homologous chimera or the B cell epitope sequence. The affinities of the anti-chimera antibodies for the B cell epitope were assessed by a fluid-phase double-isotope radioimmunoassay. All the chimeras induced good antibody responses in both strains of mice with specificity for the B cell epitope. Chimeras containing two copies of the T cell epitope induced antibodies with higher affinity for the B cell epitope than did chimeras containing one copy of the T cell epitope or two copies of the B cell epitope. Furthermore, the amino terminal location of the T cell epitope in relation to the B cell epitope in the chimera induced higher affinity anti-B cell antibody than did the reverse orientation. These results suggest that orientation of epitopes and amino acid composition of chimeric peptides affect antigen processing and presentation to T cells which govern both the specificity and affinity of antibody produced. Thus, for the production of synthetic peptide immunogens with vaccine potential, attention needs to be given to the number and orientation of the component epitopes required to produce highest affinity antibody.

The effect of orientation of epitopes on the immunogenicity of chimeric synthetic peptides representing measles virus protein sequences

We have studied the influence of the orientation of T- and B-cell epitopes on the immunogenicity of chimeric synthetic peptides in terms of the ability of the T-cell epitope to provide help for the production of antibody to the B-cell epitope. A T-cell epitope from the fusion protein of measles virus (288-302), previously shown to act as a T-helper epitope in a panel of six inbred mouse strains, was co-linearly synthesized at either the amino- or carboxyl- terminus of a B-cell epitope from the haemagglutinin of the virus (188-199) with or without the inclusion of a glycine-glycine spacer. The four chimeric peptides were used to immunize a panel of five mouse strains and induced good anti-chimera antibody responses. In general, the chimeras in which the T-cell epitope was amino-terminal to the B-cell epitope induced antibodies which bound well to the B-cell epitope whereas the carboxyl-terminal orientation of the T-cell epitope with respect to the B-cell epitope failed to induce such antibody. These latter chimeras induced the production of antibodies which preferentially bound to the T-cell epitope. The inclusion of the gly-gly spacer in the chimeras did not enhance their immunogenicity nor did it increase antibody titres to the B-cell epitope. The affinity of the anti-peptide antibodies was markedly influenced by the orientation of the epitopes in the chimeras. The antibody elicited by the peptide in which the T-cell epitope was amino terminal to the B-cell epitope had significantly higher affinity for the B-cell epitope than that induced by immunization with the peptide in the reverse orientation.