Urine test for lupus nephritis may be possible

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May 30, 2003

Urine test for lupus nephritis may be possible

Hong Kong - Patients with active lupus nephritis have significantly higher

levels of interferon- (IFN-) expression in urinary sediment than systemic

lupus erythematosus (SLE) patients without renal involvement. Measurement of

cytokine gene expression by real-time quantitative polymerase chain reaction

(PCR) may offer a noninvasive alternative to kidney biopsy for detecting

active nephritis, researchers report in the May 2003 Arthritis & Rheumatism

[1].

" The message is not that a certain gene (IFN- in this case) is up-regulated,

but that the study of gene expression in urinary sediment is technically

feasible. "

" The most important finding in this study is the elevated IFN- expression in

urinary sediment. The message is not that a certain gene (IFN- in this case)

is up-regulated, but that the study of gene expression in urinary sediment

is technically feasible. This has many potential clinical applications, "

senior author Dr Chuek-Chun Szeto (Prince of Wales Hospital, Chinese

University of Hong Kong) tells rheumawire.

RNA extraction proves surprisingly easy

Szeto and colleagues studied inflammatory cytokine gene expression in 25

patients with active lupus nephritis, 25 patients with inactive SLE and

previous renal involvement, 20 patients with inactive SLE and no history of

renal involvement, 10 patients with biopsy-confirmed noninflammatory renal

diseases, and 10 healthy volunteers.

The investigators centrifuged urine specimens at 3000 g for 30 minutes at

4°C and extracted total RNA with an RNeasy Mini kit (Qiagen, Venlo, the

Netherlands). They then used Superscript II RNase H-reverse transcriptase

(Invitrogen, Carlsbad, CA) to reverse-transcribe samples of about 0.5 g RNA

to cDNA. They quantified cytokine mRNA expression by real-time quantitative

polymerase chain reaction (PCR) using primers and probes for interleukin-2

(IL-2), IL-4, and IFN-. Levels of cytokine expression in each group were

compared with those from the healthy control group.

" I was surprised at how easily we could extract RNA from urinary sediment,

even in healthy subjects. The next question we are asking is about the

cellular origin of the RNA, " Szeto says.

IFN- much higher in active lupus nephritis

Urinary expression of IFN- was significantly higher in the patients with

active lupus nephritis compared with all of the other groups (p<0.001).

Neither IL-2 expression nor IL-4 expression clearly differentiated the

patients with active nephritis.

The level of IFN- expression in the urinary sediment also correlated

significantly with the overall systemic lupus erythematosus disease activity

index (SLEDAI) score (r=0.590, p<0.001) and with the renal SLEDAI score

(r=0.642, p<0.001).

Szeto notes that in lupus nephritis, the severity of renal damage depends on

activated T cells and macrophages, which secrete inflammatory mediators into

the kidney. Attempts to link the levels of these cytokines in sera or in

peripheral blood mononuclear cells to degree of kidney involvement have been

largely unsuccessful, because circulating cells provide a poor reflection of

local inflammation. " In essence we found a substantial elevation of IFN-, a

classic Th1 cytokine, in the urinary sediment of patients with active lupus

nephritis. Since IFN- is mainly produced by locally activated lymphocytes,

our results further support the view that lupus nephritis involves

intrarenal infiltration, activation, and alteration of the secretory

phenotype of lymphocytes toward the Th1 pathway, " the investigators write.

They also demonstrated a dose-response relationship between the degree of

Th1 pathway up-regulation and the severity of kidney involvement. Szeto

thinks that the measurement of cytokine gene expression in urinary sediment

could easily become a routine tool for monitoring the activity of lupus

nephritis. " This assay requires real-time polymerase chain reaction

performed by a LightCycler machine, which is available in many clinical and

research laboratories. Some training is needed to use the LightCycler, but

the technique is not very difficult to learn, " Szeto says.

Janis

Sources

1. Chan RW, Tam LS, Li EK, et al. Inflammatory cytokine gene expression in

the urinary sediment of patients with lupus nephritis. Arthritis Rheum 2003

May; 48(5):1326-31.