Lymphocytes and Lymphoma Flashcards
List and describe the Lymphoid system components
T cells
o Major component of cell mediated immunity
o Develop in thymus and traffic to lymph tissues
Helper T cells (CD4+)
• Recognizes Ag presented in context of MHC class II molecules
• Coordinates immune response by involving other cells
Cytotoxic T cells (CD8+)
• Kills cells presenting Ag in context of MHC class I molecules
NK Cells
o Kill cells with low MHC class I expression
o Have Fc Receptors
o Participate in antibody dependent cellular cytotoxicity
B cells
o Major cells for developing humoral immunity
o Develop in marrow and traffic to nodes/lymph tissues
• Pre-programmed when leave marrow to recognize Ag
o After recognizing Ag they self select best clones to become memory cells and plasma cells
o Plasma cells are immunoglobulin secreting cells
• IgM, IgG, IgA, IgD, & IgE
Define lymphopenia
lymphocyte count <1,000/μl
o Occurs in aplastic anemia, AIDS, certain immunodeficiency diseases, after treatment with corticosteroids and immunosuppressants, in associated with some lymphomas (advanced Hodgkin Lymphoma)
Define lymphocytosis
lymphocyte count >5,000/μl
o Children = more often reactive = occurs with acute infections: EBV-associated infectious mononucleosis and Bordetella pertussis infection
o Older adults = chronic lymphocytic leukemia
Define lymphoma
Heterogeneous group of lymphoproliferative malignancies
• Results from clonal expansion of tumor cells derived from B, T, or NK cells
• 60+ different histologic subtypes
• 85%-90% in the US are derived from B cells
Range of clinical presentations:
• Asymptomatic pick up on routine blood work
• Painless adenopathy
• Emergent medical problem
Variable natural histories, therapeutic responses, prognoses
Normal Lymphoid protein antigens
B cells: CD19, CD20, surface Ig
Plasma Cells: CD138, Cytoplasmic Ig
T cells: CD2, CD3, CD5, CD7; CD4 for helper cells and CD8 for cytotoxic T cells
NK cells: CD2, CD16, CD56; CD158 (killer inhibitory receptors/ KIRs
B-cell Biology and Lymphoma relationship:
Normal B cell response to Ag create intense genomic pressure: • More receptor editing, somatic hypermutation, and class switching → more chance for error/mutation
Most lymphomas arise from B cells which have trafficked through the germinal center
Greater Ag stimulus increases risk for the development of lymphoma:
• Chronic infections (EBV, H. pylori, Hepatitis C)
• Sjogrens syndrome, Hashimotos thyroiditis
• Environmental exposures (chemicals, pesticides, etc.)
Normal Lymph node morphology
Cortex contains primary follicles
-Contain naive B cells
Reactive = Germinal Centers:
- Surrounding mantle zone (resting B cells)
- Inner zone: proliferating B cells and somatic hypermutation –> selection –> generation of memory cells, plasma cell precursors and class switching
T cell paracortical zone
Medulla
Causes of Lymphocytosis
Infection:
-EBV, CMV, Hantavirus, early HIV, brucellosis, toxoplasmosis, TB, pertussis, other
Drug:
-Dilantin
Other:
-Smoking (polyclonal B cell lymphocytosis); post-vaccination
Endocrine:
-Thyrotoxicosis, acute stress (transient)
Malignant:
-CLL, large granular lymphocytic leukemia, peripheralization of other lymphoid malignancies like mantle cell, marginal zone, and follicular lymphoma
EBV (infectious mononucleosis): symptoms & hematologic findings
Symptoms:
• Fever, sore throat, profound fatigue, enlarged lymph nodes in neck and axillae, rash, splenomegaly, hepatomegaly (less often)
• Usually last 1-4 weeks
More complicated symptoms
• Splenic rupture, aseptic meningitis, respiratory distress from enlarged tonsils, severe hepatitis
• Rare
Hematologic findings:
• Lymphocytoiss with predominance of atypical lymphocytes = Mainly CD8+ T cells that react to EBV-produced antigens
• Anemia = rare
• Mild reduction in platelets (25% cases)
• Liver enzyme elevation (80% cases)
EBV (infectious mononucleosis): diagnosis
Monospot test
• Rapid but not very specific
• Tests for presence of heterophile Abs (released by activated B cells → agglutination of horse RBC or hemolysis of ox RBC)
Assay for anti-EBV antibodies
• More specific test
• Early in infection = rise in IgM against viral capsid antigen and Abs against “early antigen”
• Later in infection = IgG against viral capsid appears = persists for life
• After several weeks = Ab against Epstein-Barr nuclear antigen develops
Quantitative PCR assays
• EB virions in blood
EBV (infectious mononucleosis): phases & immune response
o Phases: 1) Lytic (epithelial cells, B cells) • Active viral replication and lysis • Most genes active 2) Latent (B cells) • DNA circularizes forming episome • 10 genes expressed • Viral replication a rare phenomenon • B cells are transformed (immortalized)
Immune Response
Humoral response mostly useful for dx
• Monospot test detects heterophile Abs
Vigorous cellular response keeps transformed immunoblasts under control
• CD8+ cytotoxic T cells proliferate & expand (atypical lymphs)
• CTL’s efficiently clear infected immunoblasts
Response is virtually watertight in preventing proliferation of virally transformed immunoblasts
Immune Surveillance
• Virus persists in the small resting B cell fraction
• Cells with only the EBNA 1 program
• Cells remain invisible to the immune system
• No tendency to expand, proliferate, or accumulate
In normal adults, about 1 x 106 B cells are infected
• Tends to remains stable over time
• Unless immune system disrupted
EBV (infectious mononucleosis): role in post-transplant lymphoproliferative disorders (PTLD)
- EBV driven proliferation of infected B cells
- Occurs in setting of iatrogenic T cells suppression
- Spectrum of clinically and morphologically heterogeneous lymphoid proliferations
- Proliferations progress from polyclonal to oligoclonal to monoclonal
PTLD Risk Factors
• Degree of immunosuppression
• Frequency of rejection episodes
• Risk highest first year after transplant
• Later episodes less likely to be EBV related
Important treatment is reduction in immunosuppression
Hodgkin’s Lymphoma: epidemiology
o Bimodal distribution
o Often seen in young adults
Hodgkin’s Lymphoma: pathology
o B cell lymphoma
Characteristic Reed-Sternberg cells
• Large cells with bilobed nuclei
• Large eosiniphilic nucleolus = “owl-eyed” appearance
o See RS cells in background of benign cells of mixed lineage
o May have fibrotic bands and sclerosis of lymph node capsule (Nodular Sclerosing HL)
A “crippled” germinal center B cell = can’t make functional Ig
• Somatic mutations result in stop codon (no sIg)
• No apoptotic death → malignant transformation
Does NOT have normal B cell surface antigens:
• NO CD20, CD19, CD45 (unlike most B cells)
• Express CD30
Potent cytokine producing cells → inflammatory reaction of neutrophils, eosinophils, plasma cells
o Unclear how this occurs (EBV present in 50% of cases)
o Unclear how cells end up with RS phenotype
Hodgkin’s Lymphoma: clinical features & lab findings
Often seen in young adults
• Present with painless lymphadenopathy (often in neck or supraclavicular fossa)
Wide variety of presentations • B symptoms (fevers, night sweats, weight loss) • Pruritis • Cough/SOB • Pain • Painless adenopathy
Lab findings: • Normocytic anemia • Lymphopenia • Elevated ESR • Elevated LDH
Hodgkin’s Lymphoma: staging
Typical staging results:
o Stage I: node involvement in one lymph area
o Stage II: disease involving 2 or more nodal areas confined to one side of diaphragm
o Stage III: nodal disease above and below diaphragm
o Stage IV: widespread involvement including disease outside lymph node system
o Most often disease is localized to above the diaphragm
o Common to have extensive mediastinal disease
o Tends to spread to contiguous nodal groups (Unlike NHL)
Hodgkin’s Lymphoma: treatment
o Dictated mainly by where the disease is located rather (results of staging) than the exact histologic subtype
o 4 subtypes of classical Hodgkins
For stage I and II:
• Abbreviated chemotherapy + radiotherapy
More advanced disease:
• Repeated cycles of combination chemotherapy
Hodgkin’s Lymphoma: prognosis
IPS score: o Based on number of risk factors: Age greater than 45 Male Low albumin Anemia Stage IV WBC over 15k Lymphopenia
Highly curable with current treatments (5 year survival rates):
• Stage I and II: 85-95%
• Stage III: 70-85%
• Stage IV: 55-70%
Non-Hodgkin Lymphoma (NHL): epidemiology
o Median age of diagnosis: 60 years
Non-Hodgkin Lymphoma (NHL): morphology
60ish different subtypes
• B cell (85%), T cell, and NK cell
• Histologic subtype determines patient approach
Non-Hodgkin Lymphoma (NHL): types
Often widespread disease at diagnosis Wide variation in outcome: • Some cases rapidly fatal • Some cases readily curable • Some cases incurable BUT patient can live for many years with good quality of life
Types:
Aggressive NHL
• Short natural history (patients die within months if untreated)
• Disease of rapid cellular proliferation
• Potentially curable with chemotherapy
Indolent NHL
• Long natural history (patients can live for many years untreated)
• Disease of slow cellular accumulation
• Generally incurable with chemotherapy
Non-Hodgkin Lymphoma (NHL): clinical presentation & lab findings
Aggressive NHL: Symptomatic presentation: • Palpable lymphadenopathy • B symptoms • Pain • Organ failure • Variety of other symptoms
Indolent NHL:
• Painless adenopathy
Overall: more prone to bacterial than fungal or viral infections
Lab findings:
• Coombs positive hemolytic anemia
• Ig deficiency
• Monoclonal gammopathy
Non-Hodgkin Lymphoma (NHL): staging
o History and physical
o Lab work:
• Beta 2 microglobulin = prognostic in indolent lymphomas
• LDH = prognostic in aggressive lymphomas
o CT scans
o Bone marrow biopsy
o PET scan
o CNS evaluation (lumbar puncture and CSF exam) with aggressive lymphomas
Non-Hodgkin Lymphoma (NHL): treatment
Dictated mainly by histology
• Reliable hematopathology crucial
Aggressive NHL Combinations of drugs: • Anti-CD20 agents (Rituximab) • Cyclophosphamide • Vincristine • Adriamycin • Prednisone Radiotherapy to palliate localized symptomatic disease Cure is often the goal
Indolent NHL
• Immediate treatment does not prolong overall survival for asymptomatic low tumor burden patients
• So = watch and wait approach
When to treat?
• Constitutional symptoms
• Compromise of a vital organ by compression or infiltration, particularly the bone marrow
• Bulky adenopathy
• Rapid progression
• Evidence of transformation
Patients with symptoms or high tumor burden warrant immediate treatment
Control is the goal
Non-Hodgkin Lymphoma (NHL): prognosis
Measured based on IPI (international prognostic index) stratification based on risk factors
Risk factors: • Age over 60 • Pathologic classification • Immunologic function • Stage III or IV and mass of disease • Growth rate • Site (bad prognosis = brain lymphoma) • High LDH level • Symptoms • Performance status over 1
Describe the role of chromosome translocations in the pathophysiology of follicular NHL
t(14;18)
Follicular lymphoma
o Places bcl-2 oncogene from chromosome 18 → chromosome 14 under the IgH promoter
o Result: over-expression of bcl-2 → increases apoptotic threshold = cells don’t die
• Indolent lymphoma with slow accumulation of malignant cells
Describe the role of chromosome translocations in the pathophysiology of Burkitt’s Lymphoma
t(8;14)
Burkitt Lymphoma
o Places c-myc oncogene from chromosome 8 → chromosome 14 under the IgH promoter
o Result: over-expression of c-myc → proliferation signal
• Aggressive malignancy with high growth rate
Describe the role of chromosome translocations in the pathophysiology of Mantle Cell Lymphoma
t(11;14)
Oncogene: Bcl-1
Protein: Cyclin D1
Results in increased proliferation
Describe the role of chromosome translocations in the pathophysiology of Large Cell Lymphoma
t(3;14)
Oncogene: Bcl-6
Protein: Zinc-finger TF
Results in deregulated transcription
• Aggressive
Use expression array to figure out sub-type
o Look same on histology
o BUT different outcomes:
o Germinal center B-cell like type has better survival than Activated B-cell like type
Chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL): epidemiology
o Most common adult leukemia in Western world
o Median age 68
o Affects males more than females
Chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL): clinical presentation
Often diagnosed on routine blood work
• Combination of immunodeficiency and propensity toward autoantibody mediated immune phenomena
• Ex: autoimmune hemolysis anemia; immune thrombocytopenia
o Isolated lymphocytosis
o Patients usually asymptomatic
o An indolent lymphoproliferative disease
Manifestations can include:
Marrow failure (anemia, thrombocytopenia, neutropenia)
Lymphadenopathy and splenomegaly
Recurrent infections due to impaired humoral immunity
• Decreased levels of normal immunoglobulins
T cell deficiency:
o Malignant B cells produce immunosuppressive cytokines (TFG-β)
o Also soluble cell surface receptors (CD27) = inhibit T cell function
• Increased incidence of 2nd malignancies = Carcinoma of bowel, lung, skin, prostate, and bladder
• Autoimmune cytopenias due to dysregulation of immune system
Minority of cases = transformation to large cell lymphoma
• “Richter’s Transformation”
Chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL): pathology
o Large numbers of normal-appearing small lymphocytes
o Smudge cells prominent
Characteristic immunophenotype:
Monoclonal B cells with IgM + IgD (all are either kappa or lambda light chains) and CD5 (normally a T cell antigen), CD19, low amounts of CD20 and CD23
Use flow cytometry:
• Look for kappa: lambda ratio (normally 3:1)
• Look for co-expression of CD19 with CD5 (in CLL and mantle cell lymphoma)
• Expression of CD23 (positive in CLL; negative in mantle cell lymphoma)
Chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL): treatment
If asymptomatic = not require treatment
Symptomatic
• Chemotherapy with or without Rituximab (anti-CD20 mAb)
o Incurable (except some cases after allogenic bone marrow transplant)
