The Lymphadenopathy of HIV Infection

Abstract

The increase in the number of HIV-infected patients and the progression of the disease into the acquired immunodeficiency syndrome (AIDS)' have stimulated wide-spread attention. The result has been a better knowledge of the pathogenesis of AIDS. Variations in severity at the onset and in the progression of the disease, which possibly are related to the means of infection transmission and to the health of the patient, account for the wide spectrum of clinicopathologic manifestations. It is well-documented that HIV is transmitted mainly through sexual intercourse or via blood or blood products, and three distinct pattems of the disease have been documented. 2 Histopathologic studies of the lymph nodes of HIV-positive patients have enabled the medical community to more accurately diagnose the disease

Full text

HEMATOPATHOLOGY
Review Article
The Lymphadenopathy of HIV Infection
CARLO D. BARONI, M.D. AND STEFANIA UCCINI, M.D.
The increase in the number of HIV-infected patients and
the progression of the disease into the acquired immuno-
deficiency syndrome (AIDS)1 have stimulated wide-
spread attention. The result has been a better knowledge
of the pathogenesis of
AIDS.
Variations in severity at the
onset and in the progression of the disease, which possi-
bly are related to the means of infection transmission
and to the health of the patient, account for the wide
spectrum of clinicopathologic manifestations. It is well-
documented that HIV
is
transmitted mainly through sex-
ual intercourse or via blood or blood products, and three
distinct patterns of the disease have been documented.2
Histopathologic studies of the lymph nodes of HIV-posi-
tive patients have enabled the medical community to
more accurately diagnose the disease. Furthermore,
these studies have helped to better define the course, the
histopathogenesis, and the progression of the disease.
The term persistent generalized lymphadenopathy
(PGL) has been introduced to describe a spectrum of
histologic
changes
that occur in the lymph nodes of HIV-
positive patients independently of the way of entry of the
virus and of the clinical pattern. Although the clinico-
pathologic potential of PGL was originally uncertain,
clinical, pathologic, and immunologic evidence indi-
cates that PGL usually progresses into AIDS, suggesting
that patients with PGL have an increased risk of develop-
ing AIDS.
The diagnosis of PGL largely depends on the correla-
tion between a history of exposure to HIV, clinical and
laboratory findings, and compatible pathologic fea-
tures.3"8
These findings may be suggestive of other types
of reactive lymphadenitis that are mainly virally caused,
From the
Department
of Human
Biopathology,
Section
oflmmuno-
palhology.
University
La
Sapienza,
Rome, Italy.
Received October 26, 1992; accepted for publication October 30,
1992.
Supported by a grant from Ministero della Sanita, Progetto AIDS n.
720407.
Address reprint requests to Dr. Baroni: Department of Anatomic
Pathology, Viale Regina Elena 324,
00161,
Rome, Italy.
however, such as infectious mononucleosis.9 As a result,
a number of
characteristic,
although not specific, patho-
logic features have been identified in lymph nodes re-
moved from HIV-positive patients. Furthermore,
immunohistochemistry, with its potential for demon-
strating
lineage,
function, and viral antigens,
has
contrib-
uted greatly to a better interpretation of the morphologic
features.
HISTOLOGIC FEATURES
The cervical and axillary lymph nodes of patients af-
fected
by
PGL often
are
enlarged.
They reveal three histo-
pathologic patterns, in which follicular alterations
largely prevail. Therefore, PGL may be classically sepa-
rated into three main types according to the presence of
hyperplastic or regressive changes of the lymphoid folli-
cles (Table
l).
10
"
Hyperplastic Changes
This histologic phase of PGL has been called follicular
hyperplasia with or without follicular fragmentation
(Fig. 1A). The follicles are often enlarged and increased
in number; they extend almost throughout the node. A
striking feature often is marked a variation in shape with
irregular margins. Mitoses are numerous, as are macro-
phages containing tingible bodies, which confer a starry
sky appearance. Several small blood vessels with flat en-
dothelia are often observed within the hyperplastic ger-
minal centers; they often are surrounded by small lym-
phocyte
aggregates.
Small lymphocytes also are scattered
within germinal centers as single cell infiltrates, and may
be associated with small foci of hemorrhage.
The interfollicular and paracortical areas are popu-
lated by small lymphocytes, immunoblasts, and macro-
phages. A striking feature is the presence of a marked
proliferation of arborizing postcapillary venules with
high endothelia (HEVs, Fig. IB). In the interfollicular
areas there are aggregates of monocytoid
B
lymphocytes,
akin to the condition called immature sinus histiocy-
tosis.
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398 HEMATOPATHOLOGY
Review
TABLE 1. HISTOLOGIC CLASSIFICATION OF PERSISTENT
GENERALIZED LYMPHADENOPATHY
Follicular hyperplasia
Without follicular fragmentation
With follicular fragmentation
Follicular involution
Follicular depletion
Follicular fragmentation, which may represent an
early regressive change, is indicated by foci of hemor-
rhage in germinal centers.12 At this stage of the disease,
although lymphocyte depletion is not yet prominent in
paracortical areas, mantle zones are extremely reduced
or even absent
(Fig.
1
A).
As
follicular fragmentation pro-
gresses, germinal centers are characterized by hemor-
rhages and by frequent foci of necrosis, which is asso-
ciated with small lymphocyte infiltration (Figs. 1A and
C).
The simultaneous presence, in the same node, of
hy-
perplastic and undamaged germinal centers and of
others with fragmentation (Fig. 1A) suggests on histo-
logic grounds that regressive lesions may be related to,
and perhaps follow, hyperplastic changes. The observa-
tion of cases in which biopsy specimens were taken from
two lymph nodes in subsequent periods supports this
interpretation.13 As already mentioned, a frequent
change in the sinuses is represented by sinus histiocyto-
sis.
So-called vascular sinus transformation occurs in the
peripheral sinuses less frequently.
Regressive Changes
As regressive changes progress, the involved nodes
may be classified into those with follicular involution
and those with follicular depletion (Table 1). Follicular
involution is characterized by a hypervascular follicular
pattern, with small follicles resembling those seen in
Castleman's disease. Germinal centers are remarkably
small, and show a rather typical hyaline vascular center,
which is irregularly surrounded by large, nucleolated
cells resembling follicular dendritic reticulum cells and
by a few layers of small lymphocytes. At this
stage,
arbor-
izing HEVs in the paracortical areas are remarkably nu-
merous. Lymphoid depletion often has been detected al-
ready in the paracortical
areas;
therefore, HEVs, without
the support of the normally crowded lymphocytes, be-
come particularly evident.
The most severe histologic pattern of regression is fol-
licular depletion, which always is accompanied by lym-
phocyte depletion in paracortical areas. The involved
lymph nodes may show diffuse fibrosis with total obliter-
ation of the normal architecture. Few remaining lym-
phocytes and plasma cells are observed, sometimes in
A.J.C.P. •
perivascular position. Macrophages often are evident, al-
though fibrosis is marked. This pattern of extreme invo-
lution is characteristic of the lymph nodes of AIDS pa-
tients.
IMMUNOHISTOLOGIC FEATURES
The antigenic profile of
cells
populating lymph nodes
involved by PGL, as well as the presence of viral anti-
genic products and viral nucleic acids, can be deter-
FIG.
1.
A.
Lymph node infiltrated by
PGL.
Germinal centers
are
irregu-
larly shaped with foci of necrosis and infiltration of lymphocytes. Man-
tle zones are generally absent. Notice the simultaneous presence of
undamaged and fragmented germinal centers (hematoxylin and eosin,
X40).
B.
Paracortical area showing numerous arborizing high endothe-
lial venules (hematoxylin and eosin, X250). C. Presence of a focus of
infiltration of small lymphocytes in germinal center (hematoxylin and
eosin, X250). D. Cryostat section immunostained witH OK.T8 mono-
clonal antibody. Scattered and clustered CD8+
cells
are numerous (im-
munoperoxidase, X250). E. Cryostat section stained with DRC-1
monoclonal antibody. The network of FDRCs shows several foci of
lysis (immunoperoxidase, XI25). F. Cryostat section stained with an
anti-HIV p24 major core protein monoclonal antibody. Notice the
irregular meshwork of positivity, which mimics that displayed by
DRC-1-positive FDRCs (immunoperoxidase, X250).
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BARONI AND UCCINI 399
PGL
in
HIV Infection
mined by immunocytochemistry and by in situ
hybridization. We limit the description of
the
immuno-
histologic and viral features to lymph nodes involved by
PGL with follicular hyperplasia with or without frag-
mentation, because nodes with regressive changes are
devoid of interesting immunohistologic features.
germinal centers, the CD8+ subset is characterized by
the highest expression of the proliferation antigen;
CD4+ T lymphocytes, macrophages, and FDRCs are
constantly Ki67- negative.18
Paracortkal Areas
Lymphoid
Follicles
During the hyperplastic phase, the cellular population
of germinal centers comprises mainly
CD 19+
B lym-
phocytes and a small number of CD2+ mature T lym-
phocytes.14'15 During follicular fragmentation, germinal
centers show a peculiar reduction of the number of
CD4+ T lymphocytes, which is associated with an in-
crease in the percentage of CD8+ T
cells.
Therefore, the
CD4:CD8 ratio is lower in PGL than in nodes affected
by other types of lymphadenitis.16"18 In PGL, CD4+ ger-
minal center lymphocytes are always individually scat-
tered, whereas CD8+ T lymphocytes are generally
grouped and often in a perivascular position
(Fig.
1D).
In
lymphadenitis induced by viruses other than HIV,
CD8+ T lymphocytes are irregularly scattered within
germinal centers, and generally they are not grouped in
clusters. Follicular dendritic reticulum cells (FDRCs) are
strongly DRC-1 positive; in PGL FDRCs show interest-
ing changes defined as follicular lysis,12 which correlates
well with the histology of follicular hyperplasia
(Fig.
1E).
It is therefore possible to classify FDRCs immunohis-
tologically into three basic patterns: (1) normal
DRC-1-positive network in follicular hyperplasia with-
out fragmentation; (2) moderate lysis of the
DRC-1
-posi-
tive network, with follicular fragmentation closely paral-
leling the CD8+ T lymphocyte infiltration of the
germinal centers; and (3) severe to total lysis of the DRC-
1-positive
reticulum strictly paralleling extensive follicu-
lar fragmentation, follicular involution, and deple-
tion.19,20 The hyperplastic germinal centers are
populated by numerous macrophages that stain strongly
positive for
CD
14,
slightly positive for CD4, and nega-
tive for PAM-1 and
CD
lib monoclonal antibodies.
These macrophages are also muramidase- and a-l-anti-
chymotripsine-positive. An interesting immunohistolo-
gic feature of hyperplastic germinal centers is the strong
positivity for Ki67 monoclonal antibody, which stains
proliferating
cells
in the G1-G2 phases.
A
double immu-
nostaining technique used to identify the phenotype of
the proliferating cells demonstrated that CD
19+
B lym-
phocytes make up the majority, accounting for more
than 90% of the entire germinal center cell population.
Within the T lymphocytes infiltrating the hyperplastic
In the paracortical areas of lymph nodes infiltrated by
PGL, the majority of cells are CD2+ T lymphocytes;
they are intermingled with small numbers of CD
19+
B
lymphocytes. The proportion of T-lymphocyte subsets
in paracortical areas parallels that observed in germinal
centers. Therefore, the number of CD8+ T lymphocytes
is higher than that of CD4+ T lymphocytes, explaining
the low CD4:CD8 ratio observed in paracortical areas as
well.18
As
already described, in the presence of PGL, par-
acortical areas are characterized by numerous arborizing
HEVs whose number is substantially higher than that
observed in types of lymphadenitis other than PGL. Fur-
thermore, these blood vessels often show a remarkable
expression of HLA-DR-related antigens, indicating that
these high endothelial cells have been activated.13
Adhesion molecules are involved in the adhesion of
leukocytes to the endothelium; therefore, they are ex-
pressed on the endothelial cell surface, in particular dur-
ing inflammatory reactions.21 Preliminary data,18 using
immunocytochemistry, have suggested that the expres-
sion of
the
intercellular adhesion molecule (ICAM-1) is
constantly expressed on HEVs in PGL as well as in other
types of follicular hyperplastic lymphadenitis. The endo-
thelial cell-adhesion molecule (ECAM-1) is poorly ex-
pressed both in PGL and control follicular lymphadeni-
tis,
whereas the vascular cell-adhesion molecule
(VCAM-1) is never expressed. Immunohistochemical
cytokine expression also has been investigated in lymph
nodes involved by PGL; cells expressing IL-la, IL-10,
and TNFa were rarely detected.18
Several studies have shown that proliferation and acti-
vation of
B
lymphocytes in the germinal centers repre-
sent characteristic and intriguing features of PGL during
the hyperplastic phase. These morphologic changes re-
late well with the marked hypergamma globulinemia of-
ten present during PGL. However, it has not yet been
clearly established which stimulus might be responsible
for the activation of
B
lymphocytes and polyclonal im-
munoglobulin production in the germinal center. Fur-
thermore, germinal centers represent the microenviron-
ment necessary for B-cell maturation, proliferation, and
possibly neoplastic transformation, resulting in the B-
lymphocyte lymphomas that frequently occur in AIDS
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400 HEMATOPATHOLOGY
Review Article
patients. Therefore, the evaluation, in HIV-positive pa-
tients,
of some viral agents that perhaps are able to trig-
ger the proliferation of germinal center B lymphocytes,
appears to be of interest. The presence of HIV and Ep-
stein-Barr virus (EBV) antigens and genomes has been
investigated in lymph nodes representative of the
various histologic phases of PGL. Through the use of
monoclonal antibodies raised against p24 major core
HIV protein, it has been demonstrated that p24-positive
cells are constantly present in lymph nodes of HIV-posi-
tive patients with PGL.22,23 In germinal centers p24+
cells were distributed in a reticular pattern that strictly
mimicked that of DRC-1 -positive FDRCs
(Fig.
1F).
Fur-
thermore, the similar distribution in germinal centers of
DRC-1-
and viral-antigen-positive cells also is demon-
strated by the disappearance of
the
immunostaining for
viral antigens in those germinal centers showing lysis of
the DRC-1-positive meshwork. Using in situ hybridiza-
tion, the HIV genome was demonstrated in rare and iso-
lated cells located in germinal centers and paracortical
areas in few cases of
PGL.20
The low frequency of HIV-
infected cells in PGL lymph nodes is confirmed by simi-
lar negative results obtained using Southern blot hybrid-
ization.24 The question that arises is whether other viral
agents, such as EBV, perhaps play a role in the pathogen-
esis of PGL and the subsequent lymphomatous transfor-
mation. In HIV-positive patients affected by PGL, al-
though the majority have significant anti-EBV titers,
EBV viral capsid antigen- and EBV early antigen-posi-
tive cells are detected infrequently in lymph node cells.24
Furthermore, EBV-genome-positive cells are never de-
tected either using in situ hybridization or Southern blot
analysis.24 The absence of cells expressing the EBV anti-
gens and genome in the lymph nodes of HIV-positive
patients may suggest, on morphologic grounds, that
EBV is not directly involved in the pathogenesis of ger-
minal center B-cell polyclonal activation during PGL.
Therefore, other mechanisms must be postulated. For
example, a possible role of HIV or HIV antigens in the
induction of germinal center activation, perhaps
through the action of HIV immunocomplexes presented
to germinal center B leukocytes through the accessory
cells,
may be suggested. Autoimmune mechanisms also
could contribute to the development of PGL.25,26 The
possibility that EBV might be at least partly involved in
the pathogenesis of PGL cannot be completely ruled out;
however, at such a low level, EBV could infect few cells
with few viral copies per cell. Thus, the EBV antigens
and genome are not detectable at tissue level using im-
munohistologic and hybridization techniques.
We conclude that appropriate biomorphologic corre-
lations, in terms of fine histology, immunophenotyping,
expression of adhesion molecules, cytokines, viral anti-
gens and genome, in lymph nodes involved by PGL,
would provide a clear pathologic definition of morpho-
logic changes, and further information to better define
the pathogenesis of
AIDS.
Acknowledgment.
The authors thank Maria Grazia Saladino for edit-
ing the manuscript.
REFERENCES
1.
Chin J. Current and future dimensions of the HIV/AIDS pande-
mic in women and children. Lancet 1992;2:221-224.
2.
Mann JM, Chin J. AIDS: Global perspective. N Engl J Med
1988;319:302-303.
3.
Center for Disease Control. Persistent generalized lymphadenopa-
thy among homosexual males. MMWR 1982,246-251.
4.
Brynes RK, Wing CC, Spira JJ, et al. Value of lymphadenopathy
in homosexual men. JAMA 1983;250:1313-1317.
5.
Guarda LA, Buttler JJ, Marsell P, et al. Lymphadenopathy in ho-
mosexual men: Morbid anatomy with clinical and immunologi-
cal correlations. Am J Clin Pathol 1983;79:559-568.
6. DomingoJ.Chin
NW.
Lymphadenopathy
in a
heterogenous popu-
lation at risk for the acquired immunodeficiency syndrome
(AIDS): A morphologic study. Am J Clin Pathol 1983;80:649-
654.
7.
Ioachim HL, LernerCW. Tapper
ML.
The lymphoid lesions asso-
ciated with the acquired immunodeficiency syndrome. Am J
Surg Pathol 1983;7:543-553.
8. Burns BF, Wood GS, Dorfman RF. The varied histopathology in
the homosexual male. Am J Surg Pathol 1985;9:287-297.
9. Stanley MW, Frizzera G. Diagnostic specificity of histologic fea-
tures in lymph node biopsy specimens from patients at risk for
the acquired immunodeficiency syndrome. Hum Pathol
1986;17:1231-1239.
10.
Racz P, Tenner-Racz K. Kahl C, et al. Spectrum of morphologic
changes of lymph nodes from patients with AIDS or AIDS-re-
lated complexes. Prog Allergy 1986;37:81-181.
11.
Ost A, Baroni CD, Biberfeld P, et al. Lymphadenopathy in HIV
infection: Histological classification and staging. APMIS
1989;8:7-15.
12.
Wood GS, Garcia CF, Dorfman RF, Warnke RA. The immuno-
histology of follicles lysis in lymph node biopsies from homo-
sexual men. Blood 1985;66:1092-1097.
13.
Baroni CD, Pezzella F. Stoppacciaro A, et al. Systemic lymphade-
nopathy (LAS) in intravenous drug
abusers:
Histology, immun-
ohistochemistry and electron microscopy. Pathogenetic correla-
tions.
Histopathology 1985;9:1275-1293.
14.
Modlin RL, Meyer PR, Mehlmaner
M,
et
al.
T lymphocyte subsets
in lymph nodes from homosexual men. JAMA 1983:250:1302-
1305.
15.
Said JW, Shintakn IP, Teitelbaum A, et al. Distribution of T cell
phenotypic subsets and surface immunoglobulin-bearing lym-
phocytes in lymph nodes from male homosexuals with persis-
tent generalized adenopathy: An immunohistochemical and ul-
trastructural study. Hum Pathol 1984;15:785-790.
16.
Tenner-Racz K, Racz P, Bofill M, et
al.
HTLV-III/LAV viral anti-
gens in
lymph
nodes
of homosexual men with persistent general-
ized lymphadenopathy and AIDS. Am J Pathol 1986;126:9-15.'
17.
Garcia CF, Lifson JD, Engleman EG, et al. The immunohistology
of the persistent generalized lymphadenopathy syndrome
(PGL).
Am J Clin Pathol 1986;86:706-715.
A.J.C.P.-April 1993
by guest on April 10, 2016http://ajcp.oxfordjournals.org/Downloaded from

BARONI AND UCCINI 40I_
PGL
in HIV Infection
18.
Baroni CD, Vitolo D, Monardo F, et
al.
T lymphocyte subpopula-
tions and endothelial cell activation in persistent generalized
lymphadenopathy of HIV positive patients. In: Racz P, Letvin
NL,
Gluckman JC, eds. Cytotoxic T Cells in HIV and Other
Retroviral Infections. Basel: S. Karger, 1992, pp. 118-129.
19.
Baroni CD, Uccini S. HIV and EBV expression in lymph nodes:
Immunohistology and in situ hybridization. In: Racz P, Haase
AT,
Gluckman JD, eds: Modern Pathology of AIDS and Other
Retroviral Infections: Application of Contemporary Methods.
Basel: S. Karger, 1990, pp. 99-109.
20.
Baroni CD, Pezzella F, Pezzella M, et al. Expression of HIV in
lymph node cells of LAS patients: Immunohistology, in situ
hybridization and identification of target cells. Am J Pathol
1988;133:498-506.
21.
Albelda SM, Buck CL. Integrins and other cell adhesion mole-
cules.
FASEBJ 1990;4:2868-2880.
22.
Armstrong JA, Home R. Follicular dendritic cells and virus like
particles in AIDS related lymphadenopathy. Lancet
2;1984:370-372.
23.
Baroni CD, Pezzella F, Mirolo M, et al. Immunohistochemical
demonstration of p24 HTLV-III major core protein in lymph
nodes of
LAS
patients. Histopathology 1986;10:5-13.
24.
Uccini S, Monardo F, Vitolo D, et al. HIV and Epstein-Barr virus
(EBV) antigens and genome in lymph nodes of HIV positive
patients affected by persistent generalized lymphadenopathy
(PGL).
Am J Clin Pathol 1989;92:729-735.
25.
Golding
H,
Robey
FA,
Gates III
FT,
et
al.
Identification of homolo-
gous regions in human immunodeficiency virus
I
gp4l and hu-
man MHC class II Bl domain. J Exp Med 1988;167:914-923.
26.
Strieker RB, McHugh TM, Moody DJ, et al. An AIDS-related
cytotoxic autoantibody reacts with a specific antigen on stimu-
lated CD4+ T cells. Nature 1987;327:710-713.
Vol.
99
•
No.
4
by guest on April 10, 2016http://ajcp.oxfordjournals.org/Downloaded from