I. The document summarizes several studies that investigated the role of the immune system, particularly B cells, in atherosclerosis using mouse models. II. One study found that RAG-1 deficient mice, which lack functional B and T cells, exhibited increased neointimal formation following arterial injury compared to wild type mice. Transferring B cells from wild type mice to RAG-1 deficient mice reduced neointimal formation. III. Overall, the studies suggest that B cells may play a protective role against atherosclerosis by reducing plaque formation and progression. The mechanism may involve antibodies that target oxidation-specific epitopes, but this requires further investigation.

1. Editorial Slides
VP Watch, April 17, 2002, Volume 2, Issue 15
Is B Cell Really Protective Against
Atherosclerosis?

2. • Atherosclerosis is associated with activation of immune
system.
• Atherosclerotic plaques are infiltrated by macrophages
and T lymphocytes, some of which recognize oxidized
LDL. 1,2
• Auto-antibodies to oxidized LDL and activated
components of complement cascade have been shown
in atherosclerotic plaques. 1,2

3.  In 1997, Dansky and colleagues crossed apoE-KO
mouse with RAG-1-/- (recombinase-activating gene-1) mouse,
which lacks functional T and B cells. They showed 40%
reduction of atherosclerosis in offspring chow-fed
immunodeficient mice . 9
 They also found no difference between apoE/RAG-1
KO mice on high-fat Western-type diet and those on
chow-fed in either aortic root lesion size or percent of
total aorta occupied by lesions. Fibrous plaques with
well-defined caps and necrotic cores were detected in
both Western diet-fed E- /R- and E-/R+ animals. 9

4.  Zhou and colleagues crossed apoE-KO mice with
immunodeficient scid/scid mice. They found 73%
reduction in aortic fatty streak lesions in offspring
compared with immunocompetent apoE-KO mice. 5
 By transferring CD4+ T cells from immunocompetent
apoE-KO mice to immunodeficient apoE-/- x scid/scid
mice they found that atherosclerosis increases from
27% to 79% in recipients. 5

5. Hansson et al. showed that treatment of apoE-KO
mice with intravenous immunoglobulin prevents fatty
streak development and also inhibits fibro-fatty plaques
formation in these mice through anergization of T cells
and reduction of IgM anti-oxLDL antibodies. 2
 Shah et al. found that immunization with specific
human apoB100 reduces aortic atherosclerosis,
inflammation, and alter plaque composition in apoE KO
mic. 6

6.  Unlike others, Palinski and colleagues found that
immunization of LDL receptor deficient mice with
MDA-LDL generates high titers of antibodies with
similar specificity as naturally occurring
autoantibodies. Immunized animals showed a
significant reduction in the extent of atherosclerotic
lesions. 8

7.  Caligiuri, Hansson, and colleagues discussed that
splenectomy increases extent and severity of
atherosclerosis in apoE-KO mice. 7
 Transfer of spleen cells or B cells from atherosclerotic
apoE-KO mice not only rescued the recipients but
protected them from development of advanced
atherosclerosis. They also showed that B cells from
atherosclerotic apoE-KO mice reduces extent of
atherosclerosis in splenectomized apoE-KO mice. 7
 All of the above reports provide evidence for the
role of humoral immune system in atherosclerosis.

8.  As reported in this week of VP Watch, Dimayuga,
Nilsson, and colleagues showed that periadventitial cuff
injury to carotid of RAG-1 KO mice (B and T cells
deficient) compared with wild type (with and without
high fat diet) resulted in a 4- to 5-fold increase in
neointimal formation.
 They found that B cells transfered from wild type
mice (fed normal chow or western diet) to RAG-1 KO
mice reduced carotid neointimal formation after injury,
compared with that in RAG-1 KO mice without B-cell
transfer.

9. The neointima mostly contained SMCs, with
minimal staining for monocytes/macrophages. 10
Serum cholesterol levels were not significantly
different between those groups. 10
Reconstitution of Rag-1 KO mice with B cells
from normal mice (both fed a western diet)
reduced neointimal formation up to 75%
compared the effect in Rag-1 KO mice (P<0.05).

10. Serum Immunoglobulin
0
0.5
1
1.5
2
2.5
WT D0 RAG D0 RAG Brec D0 RAG Brec D21
IgM
IgG
Serum immunoglobulins of the IgM and IgG2a isotypes were detectable in the wild type (WT)
mice before injury (WT D0). RAG-1 KO mice had no detectable immunoglobulins at the same
time point (RAG D0), but they had low IgM 48 hours after B-cell transfer (RAG Brec D0). 21 days
after B-cell reconstitution, RAG-1 KO mice had detectable serum immunoglobulins of IgM and
IgG2a isotypes (RAG Brec D21, n=4). Unreconstituted RAG-1 KO mice had no immunoglobulins
at the 21-day time point (n=2, not shown). Sera were from western diet–fed mice.
Dimayuga P, Cercek B, Oguchi S, Nordin Fredriksson G, Yano J, Shah PK, Jovinge S, Nilsson J. Inhibitory effect on arterial injury-induced
neointimal formation by adoptive B-cell transfer in Rag-1 knockout mice. Arterioscler Thromb Vasc Biol. 2002; 22: 644–649
48 hr
21 days

11. Conclusion
I. RAG-1 deficiency (lack of functional T and B cell)
causes increased neointimal formation.
II. Diet affect the response of arterial wall to injury only
when the immune system is compromise.
III. Transplanted B cells from immune competent to
immune deficient injured mice decreases
atherosclerosis.

12. Questions:
• If RAG-1 deficient (immune deficient) mice
develop significant atherosclerosis, is
atherosclerosis still an inflammatory
disease?!
• If high cholesterol level in apoE/RAG-1
deficient mice is the cause of
atherosclerosis how would you explain
plaque formation without immune
activation?

13. Questions:
• If transplanted B cells were protective
against atherosclerosis, what was the
mechanism of action, through antibodies
or what? If antibodies are the mediator
what are the antigen(s)?
• Can B cell transplant reverse
atherosclerosis or only prevents its
progression?

14. References
1) Stemme, S., B. Faber, J. Holm, O. Wiklund, J.L. Witzum, and G.K. Hansson (1995) T lymphocytes from human
atherosclerotic plaques recognize oxidized low density lipoprotein. Proc. Natl. Acad. Sci. USA. 92: 3893-3897
2) Nicoletti A, Kaveri S, Caligiuri G, Bariety J, Hansson GK. Immunoglobulin treatment reduces atherosclerosis in
apo E knockout mice. J Clin Invest. 1998; 102: 910–918
3) Hansson GK. Immune mechanisms in atherosclerosis. Arterioscler Thromb Vasc Biol. 2001; 21: 1876–90.
4) Seifert, P.S., and G.K. Hansson (1989) Complement receptors and regulatory proteins in human atherosclerotic
lesions. Arteriosclerosis. 9: 802-811
5) Zhou X, Nicoletti A, Elhage R, Hansson GK. Transfer of CD4+ T cells aggravates atherosclerosis in
immunodeficient apoE knockout mice. Circulation. 2000; 102: 2919–2922
6) Odette S. Reyes, Kuang-Yuh Chyu, Juliana Yano, Xioaning Zhao, Bojan Cercek, Sanjay Kaul, Jan Nilsson,
Prediman K. Shah; Immunization With a Novel Human Apo B100 Related Peptide Reduces Atherosclerosis and
Inflammation in Apo E Null Mice. ACC 2002-Atlanta.
7) Caligiuri G, Nicoletti A, Poirier B, Hansson GK. Protective immunity carried by B cells of hypercholesterolemic
mice. J Clin Invest. 2002; 109: 745–753
8) Palinski W, Miller E, Witztum JL. Immunization of low density lipoprotein (LDL) receptor-deficient rabbits with
homologous malondialdehyde-modified LDL reduces atherogenesis. Proc Natl Acad Sci U S A. 1995; 92: 821–
825
9) Dansky HM, Charlton SA, Harper MM, Smith JD. T and B lymphocytes play a minor role in atherosclerotic
plaque formation in the apolipoprotein E-deficient mouse. Proc Natl Acad Sci U S A. 1997; 94: 4642–4646.
10) Dimayuga P, Cercek B, Oguchi S, Nordin Fredriksson G, Yano J, Shah PK, Jovinge S, Nilsson J. Inhibitory
effect on arterial injury-induced neointimal formation by adoptive B-cell transfer in Rag-1 knockout mice.
Arterioscler Thromb Vasc Biol. 2002; 22: 644–649