The document summarizes key concepts in antibody synthesis and the physiology of the humoral immune response. It discusses: 1) B cell development from hematopoietic stem cells through transitional and mature naive B cell stages. 2) The mechanisms of immunoglobulin gene rearrangement, including V(D)J recombination and somatic hypermutation. 3) Selection processes in the bone marrow and lymph nodes that establish B cell receptor specificity and diversity. 4) The cellular interactions, molecular signaling, and genetic alterations that drive antibody class switching, somatic hypermutation, and the development of long-lived plasma cells and memory B cells in germinal centers.

1. PHYSIOLOGY OF ANTIBODY
SYNTHESIS

2. “It is not the strongest or the most intelligent who will
survive but those who can best manage change.”
Charles Darwin

4. Specificity
Diversity
Memory

8. Hematopoetic stem cell
CD34+
Pro B cell
Heavy chain
recombination starts
Pre B cell
Surface IgM+
Exposed to central
tolerance
Transitional cell
Stage1
Bcr crosslinking leads to death
Receptor of BAFF & APRIL +ve
Transitional stage 2
Bcr crosslinking leads to
proliferation
IgD+ve
Naïve b cell Marginal bcell
Mature bcell
Plasmacytes / memory
bcells
B CELL ONTOGENY

9. IMMUNOGLOBULIN GENE REARRANGEMENT

11. This can occur when hairpin loop structures
are created between the 2 strands of the DNA
following cleavage at the RSS, & a subseq.
cleavage of 1 strand creates an overhang
which acts as a Template for the addn. of
nucleotides, creating a Palindromic sequence
Nucleotides can be added in a
Nontemplated fashion (N-region
diversity, indicated by the red
nucleotides) by the enzyme terminal
deoxynucleotidyl transferase (TdT)
P-ELEMENTS AND N-REGION DIVERSITY

12. ALLELIC EXCLUSION

15. Splicing mechanism for the switch from the membrane to the secreted
form of IgM.
• Alt. processing determines whether a secreted or membrane-bound form of the μ
heavy chain is produced. If transcription termination or cleavage occurs in the intron
between Cμ4 & M secreted form is produced.
• If transcription continues through the membrane exons, then Cμ4 can be spliced to
the M seq.The hydrophobic sequence encoded by the exons M, & M2 then anchors the
receptor IgM to the membrane.

16. CD79A/ CD79B
This consists of two glycoprotein
chains called Ig-a (CD79a) & Ig-ẞ
(CD79b) . Both Ig-a & Ig-ẞ have an
extracellular immunoglobulin-type
domain, but it is their C-terminal
cytoplasmic domains which are
obligatory for signaling & which
become phosphorylated on cell
activation by antigen-induced cross-
linking of the BCR, an event also
associated with rapid Ca2+
mobilization. Tyrosine-containing
structural motifs (immunoreceptor
tyrosine-based activation motifs,
ITAMs) are present in the cytoplasmic
domains of the Ig-a/Ig-ẞ heterodimer
& it is these that undergo
phosphorylation by tyrosine kinases

17. ITAM & ITIM (IMMUNORECEPTOR TYROSINE
ACTIV./INH. MOTIF)

18. SELECTION IN BONE MARROW

20. CLOSE ENCOUNTER WITH THE OTHER KIND

21. BAFF
The cytokine milieu surrounding the B cell is
diverse & spatially and temporarily
regulated. Although B cells are modulated by
multiple cytokines, in recent years 2
members of the TNF family, BAFF & APRIL,
have emerged as key survival factors,
particularly at 2 regulatory points in
development and differentiation: the
transition from an immature to a naïve B cell
in the periphery & the survival of the newly
produced plasma cells. BAFF & APRIL are
proteins produced by cells of innate response
such as macrophages and dendritic cells, as
well as stromal cells, and are present as
membrane-bound proteins or soluble
trimers. They have 3 known receptors (BAFF-
R, TACI, and BCMA) that are present on the
membrane of B cells from the T2 stage to
their final differentiation to plasma cells

22. EVENTS INSIDE LYMPH NODE

25. AID dependent
mutator
complex
DNA replication
error
ATG ... GGC TAT GCT CAC CGT ...
V CH1
T ...GGC, CCT...
Met ... Gly Tyr Ala His Arg ... ...Gly, Pro...
AID = Activation Induced Deaminase
(-> deaminates Cytosine on Uracil
-> repair proteins then come in and this leads to error prone repair)
-> mutations are actively induced in the V-regions of the
antibody heavy and light chain genes
Val
SOMATIC MUTATION OF IG V REGION IN GC B CELL

26. ATG ... GGC TAT GTT CAC CGT ...
Met ... Gly Tyr Val His Arg ...
T
Val
...GGC, CCT...
...Gly, Pro...
V CH1
-> now encodes antibody molecule with slightly altered antigen
binding site
-> sometimes, by chance, this site will have an improved ability
to bind the inducing antigen (i.e. a higher affinity)
SOMATIC MUTATION OF IG V REGION IN GC
B CELL

27. An antigen eye view of
immunoglobulin paratope
before & after SHM

29. THE CHEMOKINE TRAIL….

31. CLASS SWITCH RECOMBINATION
Class switch
recombination is
achieved by a
recombination process
which utilizes the
specialized switch
sequences ( ) and
leads to a loss of the
intervening DNA loop
(μ, δ and γ3).

34. 1ARY & 2NDARY ANTIBODY RESPONSE

36. THE CELL THAT DOES’NT FORGET
Fanum in 1847 described a measles
epidemic on the Faroe Islands in the
previous year in which almost the
entire population suffered from
infection except for a few old people
who had been infected 65
years earlier!!
While this evidence favors the long half-life hypothesis, memory function of B-cells
transferred to an irradiated syngeneic recipient is lost within a month unless antigen is
given or the donor is transgenic for the bcl-2 gene (remember that signals in the germinal
center which prevent apoptosis of centrocytic B-cells also upregulate bcl-2 expression). It is
envisaged that B-cell memory is a dynamic state in which survival of the memory cells is
maintained by recurrent signals from follicular dendritic cells in the germinal centers, the
only long-term repository of antigen.

37. memory B cells ingest antigen and express
Peptide MHC class II fragments. After
antigen presentation of peptide to helper
T cells, memory B cells undergo expansion
and may differentiate to plasma cells.
Memory cells respond to antigen much faster,
require lower amounts of antigen, and can
even be induced in its absence by soluble
mediators such as IL-2 or IL-15, in part because
the BCR is already localized to lipid rafts.
in humans they are distinguished by the
presence of the marker CD27
The CD40-CD40L interaction contributes to directing GC B cells to mature into long-lived
memory B cells. The exact life span of memory B cells is unknown. It has been postulated that
these B cells either persist throughout the lifetime of the host or are renewed constantly
through either nonspecific or antigen specific stimulation.
MEMORY B
CELL
MEMORY B CELL

38. IGA AND IT’S ROLE IN MUCOSAL IMMUNITY

39. The mechanism of IgA
secretion at which drives the
transport of IgA dimers to the
mucosal surface .

40. TRANSCYTOSIS OF IgG

41. BACTERIAL INFECTION

42. EVASION OF HUMORAL IMMUNITY BY VIRUSES
Changing
antigens
Influenza (antigenic drift & shift), rhinovirus (protected
site)
Mutation can
produce
antagonistic T-
cell epitopes
HBV(Mutations which modify residues critical for
recognition by MHC or TCR may generate partial agonists
that can induce a profound and long-lasting state of T-cell
anergy)
Antigen
processing
EBV(EBNA- 1 inhibits Proteasome mediated processing of
the virus), HSV(Peptide binding to TAP is prevented by
ICP47), CMV(US6 prevents peptide transport through the
TAP pore)
Sabotaging of
humoral
immune
response
Pox viruses (via VCP) & HSV 1 (via surface glycoprotein),
HHV6& measles(use cd55 as receptor), echo & coxsackie (
use cd46 as receptor), (HSV) types 1 and 2, coronavirus
(bind immunoglobulin by Fc receptors)

43. ANTIBODY DEPENDENT ENHANCEMENT
DENGUE
HIV
INFLUENZA
ENTEROVIRUS/ DIABETES

44. INTESTINAL PARASITES- A DAILY WAR
The parasite is 1st
damaged by IgG antibody passing
into the gut lumen, perhaps as a
consequence of IgE-mediated
inflammation & possibly aided by
accessory ADCC cells. Cytokines
released by antigen-specific
triggering of Tcells stimulate
proliferation of goblet cells and
secretion of mucous materials,
which coat the damaged worm &
facilitate its expulsion from the
body by increased gut
motility induced by mast cell
mediators, such as LT-D4, &
diarrhea resulting from inhibition
of gluc dependent Na+ absorption
by mast cell-derived histamine
&PGE.

46. CONCEPT OF CONJUGATED VACCINE

47. CONTD.

49. IVIG

50. TOLERANCE OF ADAPTIVE IMMUNITY

51. AUTOIMMUNITY & BCELL

52. CHRONIC INFLAMMATION
leads to the release of
soluble mediators such as
the chemokines CCL21&
CXCL12, which recruit
lymphocytes
These cells, once activated, secrete
cytokines such as lymphotoxin that
act in a paracrine manner &
contribute to the organization of a
GC-like structure that includes a
dark and light zone with local
induction of AID
In contrast to the GC of the
secondary lymphoid organs,
these structures are not
encapsulated
The B cells in these structures, therefore, are continuously exposed both to the local
antigens that might be absent from the lymphoid organs & to the inflammatory
μenvironment that may facilitate bypass of the regula-tory points in B cell differentiation,
hence contributing to a potential autoimmune bias in these sites
TERTIARY FOLLICLES & AUTOIMMUNITY

53. THE IDIOTYPIC NETWORK THEORY