3C Tissues

Primary immunological consequence of absent lymph nodes

Impaired initiation of adaptive immune responses

Key immune process occurring in lymph nodes

Antigen presentation to naïve T and B cells

Most affected response in lymph node agenesis

Primary adaptive immune responses

How antigens normally reach lymph nodes

Through afferent lymphatic vessels

Cell type primarily primed in lymph nodes

Naïve T lymphocytes

Effect of lymph node absence on humoral immunity

Reduced antibody responses

Why lymph nodes are critical for immune surveillance

They concentrate antigens and lymphocytes

Primary role of bone marrow in immunity

Hematopoiesis and B cell maturation

Immune consequence of bone marrow suppression

Leukopenia affecting innate and adaptive immunity

Which innate cells are reduced in leukopenia

Neutrophils and monocytes

Which adaptive cells are reduced in leukopenia

B and T lymphocytes

Effect of leukopenia on infection susceptibility

Increased bacterial and viral infections

Role of L-selectin in T cell homing

Mediates naïve T cell rolling on HEVs

Consequence of L-selectin deficiency

Reduced T cell entry into lymph nodes

Effect of impaired HEV entry on immunity

Decreased T cell activation

Alternative adhesion molecules in homing cascade

Integrins and ICAMs

Step of adhesion cascade affected by L-selectin loss

Rolling

Primary immunological role of the spleen

Defense against blood-borne pathogens

Immune cells activated in splenic white pulp

B and T lymphocytes

Why encapsulated bacteria are dangerous post-splenectomy

Lack of opsonization and clearance

Most affected pathogens after splenectomy

Streptococcus pneumoniae

Functional similarity between spleen and lymph nodes

Organization of adaptive immune responses

Affected lymphoid structure in poorly organized lymph nodes

Germinal centers

Primary function of germinal centers

Affinity maturation and class switching

Key leukocytes in germinal centers

B cells and T follicular helper cells

Effect of defective germinal centers

Low-affinity antibodies

Impact of disrupted lymph node architecture

Impaired lymphocyte circulation

Why architecture matters in lymph nodes

Ensures proper cell-cell interactions

Effect of neonatal thymectomy

Severe T cell immunodeficiency

Effect of adult thymectomy

Minimal immediate immune impact

Reason neonatal thymectomy is severe

T cells are not yet established

Source of peripheral T cells in adults

Existing mature T cell pool

Primary function of thymus early in life

Establishment of T cell repertoire

Key difference between central and peripheral tolerance

Central occurs in thymus

Step 1 of defense against pathogens

Physical and chemical barriers

Examples of physical barriers

Skin and mucosal epithelium

Step 2 of defense against pathogens

Innate immune recognition

Cells involved in innate recognition

Macrophages and dendritic cells

Step 3 of defense against pathogens

Adaptive immune activation

Cells initiating adaptive immunity

Antigen-presenting cells

Where adaptive immunity is initiated

Secondary lymphoid organs

Importance of leukocyte trafficking in immunity

Connects antigen detection to response

Why immune responses fail without trafficking

Cells cannot reach correct locations

Integration of innate and adaptive immunity

Antigen presentation and cytokine signaling

Clinical hallmark of trafficking defects

Recurrent infections despite normal cell counts

Why chemokine gradients are essential

Provide directional migration signals

Failure of S1P signaling leads to

Lymphocyte retention in lymph nodes

Overall consequence of impaired recirculation

Reduced immune surveillance