Lymphoma & Myeloma Flashcards
What is the product of antigen-independent B-cell differentiation?
what surface markers does it have?
naïve B-cell which is capable of responding to antigen
it expresses:
complete surface IgM and IgD
pan B-cell markers - CD 19, 20, 22, 40, 79a
complement receptors
CD23 and some express CD5
What type of antibody gene do naïve B-cells have?
they have a rearranged but unmutated Ig gene
each B cell is committed to a single light chain (kappa or lambda)
In which locations does B cell development occur?
B cell activation occurs in the secondary lymphoid organs, such as the spleen and lymph nodes
After B cells mature in the bone marrow, they migrate through the blood to the SLOs
By which 2 ways can mature antigen-naïve B cells be activated?
they can be activated by antigens directly
(they apoptose or differentiate into short-lived plasma cells with production of IgM antibody of the primary immune response)
or with the input of T cells
What is a germinal centre?
What type of cells are present here and where do they originate from?
naïve B-cells develop into proliferating IgM expressing B-cell blasts
these have encountered antigen in the paracortex or T-cell zone
they migrate into the centre of the primary follicle to form a germinal centre
the germinal centre is formed from 3-10 naïve B-cells and eventually contains 10,000 - 15,000 B-cells
What are the 4 steps involved in naïve B-cells becoming plasma or memory B cells?
- proliferation
- immunoglobulin somatic hypermutation and class switch
- selection
- differentiation
What happens to the naive B cell following antigen stimulation?
What is the rate of the cell cycle like in the product?
B cells differentiate into centroblasts
these accumulate in the dark zone of the germinal centre
they are highly proliferative with a cell cycle that is completed within 6 - 12 hours
What genes are downregulated within centroblasts?
What is the result of this?
anti-apoptotic genes are downregulated
e.g. BCL-2
pro-apoptotic molecules are present
e.g. CD95
this means only cells which generate highly specific receptors to the antigen in the germinal centre will survive
What is the purpose of somatic hypermutation of centroblasts?
Where does this occur?
somatic hypermutation of the Ig V-region genes of centroblasts occurs within the germinal centre
this increases intraclonal diversity
what do centroblasts mature into?
Where are they found and which process occurs here?
centroblasts mature to non-proliferating centrocytes
these are found in the light zone of the GC
heavy-chain class switch occurs here to alter the Ig constant regions to IgG, IgA or IgE
What happens after heavy chain class switching depending on the centrocytes Ig gene mutation?
if a centrocyte’s Ig gene mutation results in a lower affinity antibody for the antigen, it undergoes apoptosis
if the gene mutation results in increased affinity, the antibody can bind to the antigen
(up until now, this has been trapped by complement receptors on follicular dendritic cells)
What happens once the centrocyte antibody has bound to the antigen?
the centrocytes process the antigen and presents it to T-cells
T-cells express the CD40 ligand
this binds to the B-cell CD40 and rescues it from apoptosis
what is required for differentiation post-GC?
inactivation of BCL6
What step in terminal differentiation is involved in the pathogenesis of Burkitt lymphoma?
downregulation of the myc gene
What is the main mechanism which inactivates BCL6?
the CD40 - CD40 ligand interaction stimulates centrocyte expression of IRF4
IRF4 represses BCL6
BCL6 has an inhibitory effect on BLIMP1, so this is upregulated when BCL6 is downregulated
WHat is the consequence of upregulation of BLIMP1?
BLIMP1 represses PAX5, enabling plasma cell differentiation
it also upregulates XBP1, which helps to regulate plasma cells in their secretory phenotype
What are the different molecules involved in plasma cell development?
- interferon regulatory factor 4 (IRF4)
- B-lymphocyte induced maturation protein 1 (BLIMP1)
- X-box binding protein 1 (XBP1)
- paired box protein 5 (PAX5)
- MYC - a regulatory gene which codes for a transcription factor
What are immunoglobulins?
When are they produced?
They are glycoprotein molecules
they are produced by plasma cells in response to an immunogen
What is the composition of immunoglobulins like?
they are composed of 2 heavy chains and 2 light chains
they are held together by covalent disulphide bonds
each chain has one variable and one constant region
How are immunoglobulins classified?
according to the amino acid sequences in the constant region of the:
heavy chains:
- IgG, IgM, IgA, IgD, IgE
light chains:
- kappa or lambda
What is protein electrophoresis?
What 5 major fractions are normally identfied?
the laboratory technique whereby serum is placed in a gel and exposed to an electric current
5 major fractions normally identified:
- serum albumin
- alpha-1 globulins
- alpha-2 globulins
- beta globulins
- gamma globulins
When is immunofixation performed?
What can it detect?
it is performed when “M-spike” is seen on electrophoresis
it enables the detection and identification of monoclonal immunoglobulins
What is the process involved in immunofixation?
serum or urine is placed on a gel and electric current is applied to separate the proteins
anti-immunoglobulin antisera is added to each migration lane
if the immunoglobulin is present, a complex precipitates
What is myeloma?
What is it preceeded by?
an incurable malignant disorder or clonal plasma cells
it is preceeded by asymptomatic MGUS in all patients
What is MGUS?
monoclonal gammopathy of undetermined significance
it is a condition in which an abnormal protein (a monoclonal protein) is present in the blood
What is the median age at presentation of myeloma?
Which groups have a higher incidence?
median age at presentation is 70 years
higher incidence in Afro-Carribean ethnic groups
Where does myeloma lie on a spectrum of plasma cell dyscrasias?
What are these called?
myeloma is one of a spectrum of plasma cell dyscrasias called paraproteinaemias
this is the presence of excessive amounts of myeloma protein or monoclonal gamma globulin in the blood
What is the diagnostic criteria used for myeloma?
IMWG diagnostic criteria
clonal bone marrow plasma cells >/= 10% or biopsy-proved bony / extramedullary plasmacytoma
and any one or more of:
CRAB features
MDEs
What are the CRAB features in myeloma?
C - hypercalcaemia:
- > 2.75 mmol / L
R - renal insufficiency:
- creatine clearance < 40 ml / min or serum creatinine > 177 micromol / L
A - anaemia:
- Hb < 100 g / L
B - bone lesions:
- one or more osteolytic lesions on skeletal radiography, CT or PET/CT
What is meant by MDEs in myeloma?
What are the 3 MDEs?
myeloma defining events
- >/= 60% clonal plasma cells on bone marrow biopsy
- SFLC ratio > 100mg / L provided the absolute level of involved LC is > 100 mg / L
- > 1 focal lesion on MRI measuring > 5mm
What % of myeloma patients have renal insufficiency at diagnosis?
How many will develop this and need treatment?
20-25% have renal insufficiency at diagnosis
50% will have renal insufficiency at some point during their disease course
2-12% will require RRT
What are the 9 external factors that can influence renal insufficiency?
- renal vein thrombosis
- bisphosphonates
- hypercalcaemia
- ACE inhibitors
- dehydration
- NSAIDs
- CT contrast
- hyperviscosity
- type 1 cryoglobulinaemia
What are the clinical features of renal insufficiency as part of myeloma?
- confusion
- poor appetite
- thirst
- chest infections
- breathlessness
- polyuria or oliguria / anuria
- peripheral oedema
- constipation
- pathological fractures
- nausea
- bone pains
What are the 3 main blood tests performed when investigating myeloma and why?
full blood count - Hb, WBC, platelets & blood film:
- looking for anaemia? active infection?
- degree of bone marrow infiltration
- rouleaux
U&Es - urea, creatinine, sodium, potassium:
- looks for renal failure & dehydration
calcium:
- is it elevated?
What is meant by rouleaux?
stacks or aggregations of red blood cells
they form due to the unique discoid shape of the RBC