WBCs, the Spleen, and Overview of the Immune System Flashcards
Immune System Functions
protection from foreign substances
tumor surveillance
self recognition
Components of the immune system
Tissues: bone marrow, thymus, spleen, lymph nodes
Cells: leukocytes, macrophages, antigen presenting cells
Proteins: immunoglobulins, complement proteins
The Complement System
Name derived from initial description as an effector arm of the immune system to “complement” antibody mediated immunity
Main functions: protect intravascular space from bacterial infection, clear tissue debris, wound healing
Tend to decrease in autoimmune disease
Humoral Immunity vs. Cellular Immunity
Humoral Immunity
- B cells –> plasma cells –> antibodies
Cellular Immunity
- T cells –> directly cytotoxic, activate phagocytes (neutrophils), direct humoral immune response (tell B cells what to do)
Immune Deficiency
Congenital
- B cell defects
- T cell defects
- Combined defects (SCID)
Acquired
- HIV
- Malignancy (CLL, lymphoma, myeloma)
- Chemo, radiation therapy
Normal Functions of the Spleen
**Hematopoiesis **
- Major site of hematopoiesis during fetal life, but becomes dormant at birth.
- Extramedullary hematopoiesis (i.e. bone marrow disease and chronic hemolytic anemias) can result in splenomegaly
Filtering
- Removal of senescent and poorly deformable RBCs that can’t tolerate the acidic, hypoxic, and hypoglycemic environment of the spleen (moves through very slowly)
- Removal of particles from RBCs such as nuclear remnants (Howell-Jolly bodies) and insoluble globin (“bite cells”)
Immune Defense
- Large lymphoid organ (50% of total Ab producing B cells)
- Sinusoids clear bacteria from circulation, mononuclear phagocytes process foreign material, stimulating antibody production by plasma cells
- Particularly important in defense agianst encapsulated bacteria - H. flu, S. pneumo, N. meningitidis
Spleen Size
On average is 13cm
15% of children have palpable spleens without evidence of illness
Involutes with age - palpable spleen in older adults is more likely to be associated with disease
Scanomegaly - may have modestly enlarged spleen that is not palpable that is not clinically or diagnostically significant.
MC causes of Splenomegaly
liver disease, hematologic malignancy, infection
Consequences of Splenectomy
Howell-Jolly Bodies
Infection Risk
Leukocytosis
Thrombocytosis
(Because normally 1/3 of WBC and plt in spleen, so once removed these are circulating. No consequence, but be aware of when reading labs)
Post Splenectomy Sepsis
Uncommon but high mortality
Highest incidence in children who have splenectomy during infancy and in lymphoma patients receiving chemotherapy
MC’ly occurs 3 years post splenectomy
Classically caused by encapsulated bacteria: *s. pneumo (MC & most fatal), h. flu, n. meningitidis *
May follow U/LRI but can develop precipitously wihtout any prior symptoms
Prevention of PSS
**Vaccines: **
- pneumococcal, H flu, meningococcal and influeza vaccine should be administered
Antibiotic ppx:
- children should receive penicillin or amoxicillin PO ppx until 5y.o or until 3 years post splenectomy
- Highly immunocompromised individuals may be considered for ppx until 18 y.o.
- adults should not receive ppx because low incidence of PSS and antibiotic resistance
- Life long ppx for all survivors of PSS
Empiric antibiotic therapy for febrile illness
- use aggressive management of any febrile illness with empiric therapy
- Antibiotics should be readily available (at home) and taken at first sign of febrile illness (amoxicillin-clavulanate, cefuroxime, or fluoroquinolone)
- After taken first dose, should proceed to the nearest health care facility
- Empiric therapy should be continued for 7-10 days
WBCs (Types)
Neutrophils
Lymphocytes
Monocytes
Eosinophils
Basophils
Neutrophils
AKA polymorphonuclear cells (PMNs)
50-75% of total WBCs
Function:
- find, ingest, and kill invading organisms
- bactericidal activity occurs when granules release hydrogen peroxide, superoxide, etc.
- will damage tissues they infiltrate (i.e. ARDS after respiratory infection) because not specific
Think BACTERIA if elevated
Appearance:
- Mature - multilobulated nucleus
- Immature are “band form” (no segmentation yet) = left shift
Neutrophils
(factors that increase or decrease)
Increase Neutrophils
- bacterial infection
- physiologic stress (i.e. surgery - doesn’t necessary have to be infection!)
- corticosteroids (1/2 are hanging out on BV walls, steroids make cells begin to circulate)
Decrease Neutrophils
- Viral infection (inverse relationship with lymphocytes)
- Drugs/toxins
Relationship between absolute neutrophil count (ANC) and risk of infection (nl > 1500). How you know when its safe to give more chemo:
ANC > 500/ul = little risk (nl infx fighting ability)
ANC 100-500/ul = significant risk
ANC < 100/ul = great risk
Lymphocytes
20-40% of total WBCs
Inc’d in most **viral infections **
Essential in the generation and regulation of immune responses
Circulate in blood, and also populate lymphoid tissues (lymph nodes, spleen)
Types:
- B cells: differentiate into plasma cells which synthesize immunoglobulins (antibodies)
-
T cells:
- Helper (inducer) T Cells (CD4+) regulators of the immune response, influenc eproduction of antibodies by B cells (HIV)
- Cytotoxic/suppresor T cells (CD8+): recognize and kill virus infected/foreign cells; down regulate antibody production by B cells
- NK cells: important in preventing growth and spread of *tumors *
