Approval Sheet CD4+ T cell affinity in autoimmunity and viral infection Open Access

Sabatino Jr., Joseph (2010)

Permanent URL: https://etd.library.emory.edu/concern/etds/dz010q68g?locale=en
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Abstract

CD4+ T cell affinity in autoimmunity and viral infection
By Joseph J. Sabatino, Jr.

Cellular immunity is mediated by engagement of the T cell receptor (TCR) with specific
peptide:MHC (pMHC) antigen leading to the induction of T cell effector functions. The
affinity of the TCR for antigen is believed to be a critical determinant for antigen-
specificity. The existing models of clonal selection and affinity maturation posit that the
highest affinity T cells dominate in a polyclonal T cell response. However, the minimal
affinity required for T cell activation is unknown, therefore it is unclear to what extent
low affinity T cells contribute to polyclonal T cell responses. Moreover, although it is
postulated that T cells specific for self- and foreign-antigens differ in their respective
affinities due to tolerance, it is unclear whether this is in fact the case. The answers to
these vital questions have been hindered by the lack of sensitive techniques for the
measure of individual T cells that comprise a polyclonal antigen-specific T cell
population. Using a highly sensitive two-dimensional (2D) binding assay, the affinities
of CD4+ T cells specific for central nervous system (CNS)-derived antigen and a viral-
antigen were compared. These studies revealed that the autoreactive CD4+ T cells were
overall of lower affinity than those specific for viral-antigen, underlying their differences
in detection by pMHC II tetramers. Remarkably, the majority of CD4+ T cells in CNS
autoimmune disease were cross-reactive for myelin- and neuronal-antigens, yet were
primarily of low affinity. However, an extensive degree of T cell affinity diversity was
observed in all polyclonal CD4+ T cell responses, suggesting that a range of low to high
antigen-specific T cells is a hallmark of cellular immunity. These findings indicate that
polyclonal CD4+ T cell responses are larger than previously believed and challenge the
existing paradigms of T cell affinity in immunity. T cell affinity may therefore play a
crucial role in the initiation, duration, and modulation of polyclonal T cell responses,
which may critically alter the outcome and treatment of autoimmunity and infection.

Table of Contents

Table of Contents
Chapter 1

: Introduction……………………………………………………………….1-25
Figure 1.1: Alteration of TCR or MHC contact residues distinguishes altered peptide
ligands and MHC variant peptides…………………………………...…………………..26
Figure 1.2: MOG35-55-induced EAE disease course……………………………...............27
Table 1.1: Comparison of TCR:pMHC kinetics to other receptor-ligand
interactions……………………………………………………………………………….28
Table 1.2: Summary of commonly used EAE models…………………………………...29
Table 1.3: Summary of altered peptide ligand therapies in EAE………………………..30
Table 1.4: Summary of MHC variant peptide therapies in EAE………………...............31
Chapter 2: Loss of IFNγ enables the expansion of autoreactive CD4+ T cells to induce
EAE by a non-encephalitogenic myelin variant antigen……………………………..32-49
Figure 2.1: IFNγ -/- and IFNγR -/- mice develop significant EAE following 45D
immunization…………………………………………………………………………….50
Figure 2.2: 45D induces significant lymphocyte infiltration in the CNS of IFNγ -/- and
IFNγR -/- mice…………………………………………………………………………...51
Figure 2.3: MOG tetramer-positive CD4+ T cells are found in the CNS of 45D-
immunized IFNγ -/- and IFNγR -/- mice………………………………………………...52
Figure 2.4: Splenocytes from 45D-immunized IFNγ -/- and IFNγR -/- mice proliferate
significantly in response to MOG 35-55…………………………………………………53
Figure 2.5: Loss of IFNγ increases absolute numbers of MOG:I-Ab tetramer positive
CD4+ T cells in the periphery…………………………………………………………....54

Figure 2.6: CD4+ T cells from 45D-immunized IFNγ -/- and IFNγR -/- mice do not
demonstrate an enhanced IL-17-secreting phenotype…………………………………...55
Table 2.1: EAE incidence, average severity and day of onset in wild-type, IFNγ -/- and
IFNγR -/- mice immunized with MOG or 45D………………………………………….56
Chapter 3: High prevalence of low affinity peptide:MHC II tetramer-negative effectors
during polyclonal CD4+ T cell responses……………………………………………57-70
Figure 3.1: Tetramer versus 2D detection of polyclonal MOG35-55 and GP61-80 CD4+ T
cells…………………………………………………………………………………...71-72
Figure 3.2: TCR levels of MOG35-55 and GP61-80 CD4+ T cells…………………………73
Figure 3.3: Kinetics of maximal adhesion frequency ( Pa) of polyclonal CD4+ T
cells………………………………………………………………………………………74
Figure 3.4: 2D affinity and antigen-specificity of tetramer-positive and tetramer-negative
CD4+ T cells………………………………………………………………………….75-76
Figure 3.5: Sorting of CD4+ T cells by tetramer binding………………..........................77
Figure 3.6: Dominance of pro-inflammatory low affinity myelin-reactive CD4+ T cells
during EAE………………………………………………………………………………78
Figure 3.7: Low affinity viral-specific CD4+ T cells contribute significant effector
responses during LCMV infection……………………………………………………….79
Chapter 4: Low affinity cross-reactive myelin- and neuronal-antigen-specific CD4+ T
cells predominate during CNS autoimmunity………………………………………..80-96
Figure 4.1: Functional cross-reactivity of 2D2 TCR transgenic and polyclonal CD4+ T
cells………………………………………………………………………………………97

Figure 4.2: pMHC II tetramer detection of MOG35-55 and NF-M15-35-specific CD4+ T
cells……………………………………………………………………………………....98
Figure 4.3: MOG and NF-M tetramer co-staining of polyclonal CD4+ T
cells………………………………………………………………………………………99
Figure 4.4: 2D binding analysis of 2D2 and polyclonal MOG35-55 and NF-M15-35 CD4+ T
cells……………………………………………………………………………………..100
Figure 4.5: pMHC II tetramer and functional reactivity of MOG35-55 and NF-M15-35 CD4+
T cells in the CNS during EAE…………………………………………………………101
Figure 4.6: High frequency of low affinity MOG and NF-M cross-reactive CD4+ T cells
in the CNS during peak EAE…………………………………………………………...102
Figure 4.7: Effect of sequential MOG:IAb and NF-M:IAb binding on the adhesion
frequency of CD4+ T cells…………………………………………………...................103
Figure 4.8: Stimulation of MOG35-55 CD4+ T cells in vitro increases cross-reactivity to
NF-M…………………………………………………………………………………...104
Chapter 5: Discussion…………………………………………………………….105-115
Figure 5.1: Proposed model of the consequences of polyclonal T cell affinity diversity in
polyclonal immune responses…………………………………………………………..116
References…………………………………………………………………………117-139




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