Page 137 - Concise Pathology for Exam Preparation ( PDFDrive )

122 SECTION I General Pathology

(c)
Decreased CD41 T cell count (,200 CD41 T cells/µL) and reversal of T4:T8 ratio
(d)
Thrombocytopenia
Increased b2 microglobulin level
(e)
(f)
Lymph node biopsy:
(i)
Early stage
- Marked follicular hyperplasia
- Follicles extend to medulla and sometimes spread outside the capsule
- Mantle zone thinned out and germinal centres seem to merge with the in-
terfollicular areas
- Presence of monocytoid B cells in and around sinusoids and in trabecular
blood vessels
- Involvement of the B cell areas of the lymph node supports polyclonal B cell
activation and hypergammaglobulinaemia
(ii)
Disease progression
- Severe follicular involution
- Follicles are depleted of cells
- Organized network of follicular dendritic cells disrupted
- Germinal centres become hyalinized
- Atrophic and small lymph nodes (burnt out appearance)
- In this stage, lymph nodes may harbour opportunistic infections
- The inflammatory response to infections in both nodal and extranodal sites
may be atypical and sparse, eg, granulomatous response to mycobacteria
may not develop adequately because of deficient CD41 T cells.
2.
Specific tests
(a)
Antigen detection
(i) Acute illness/seroconversion stage: p24 antigenaemia and viraemia, also ap-

pearance of IgM thereafter

(ii) Asymptomatic phase: decreased or absent free p24, but antibody-bound p24
antigen may be demonstrated

(iii) Clinical disease: increased free p24 antigen
�
Method: Antigen-capture ELISA
�
In the first few weeks after infection and in terminal phase, the test is uniformly positive.
Antibody detection
(b)
(i) Simplest and most widely used method

(ii) Negative in window period that follows infection (time taken for antibodies to

appear); IgM appears first followed by IgG
(iii) ELISA:

- Sensitive but not so specific
- Types used: ‘Direct solid phase antiglobulin ELISA’ and ‘Capture ELISA spe-
cific for IgM antibody’

(iv) Western blot test: more specific than ELISA

(v) PCR: Now ‘new gold standard’ test for diagnosis in all stages of HIV
(c)
Direct virus isolation and culture in neoplastic T cell line

mebooksfree.com