Analysis of HIV-related factors and coinfections based on ANY serostatus revealed a higher seropositivity rate in patients with CD4 T cells/mm3 less than 200 than greater than 200 (53% versus 33%; OR, 2.34; 95% CI, 1.37-4.02; P = 0.002), HIV copies/mL greater than 400 than less than 400 (42% versus 32%; OR, 1.70; 95% CI, 1.09-2.65; P = 0.019), with than without syphilis (56% versus 34%; OR, 2.48; 95% CI, 1.28-4.79; P = 0.007), and with than without hepatitis (47% versus 33%; OR, 1.76; 95% CI, 1.07-2.90; P = 0.027) (Table 1). No association was found between KSHV seropositivity and any comorbid conditions (data not shown).
The association of CD4 T cell count and HIV load with KSHV seropositivity persisted when serostatus was defined by ORF65 but not by LANA and BOTH , indicating ORF65 seropositivity as the main contributing factor (Table 1). A higher seropositivity rate was also found in patients with duration of HIV infection greater than 15 years than less than 15 years when defined by ORF65 serostatus (40% versus 25%; OR, 2.47; 95% CI, 1.35-4.50; P = 0.003).
We analyzed the interactions of variables. When adjusted for other factors, lower CD4 T cell count remained as a risk factor for ORF65 and ANY serostatus (data not shown). Association of HIV load with ORF65 and ANY serostatus was not affected by duration of HIV infection and CD8 T cell count but disappeared after adjusting for CD4 T cell count. Association of duration of HIV infection with ORF65 serostatus was not altered by other factors. In contrast, association of Hispanic status with ORF65 serostatus disappeared after adjusting for other factors. Interestingly, Hispanics had lower CD4 and CD8 T cell counts than non-Hispanics (P < 0.001 and 0.025, respectively), but no difference was found for HIV load and duration of HIV infection (see Figure 1A, Supplemental Digital Content 2, http://links.lww.com/QAI/A105). Lower CD4 T cell count persisted in Hispanics regardless ORF65 serostatus (P = 0.004 and 0.001, respectively) and in ORF65+ patients regardless of Hispanic status (P < 0.001 and 0.001, respectively) (see Figure 1B, Supplemental Digital Content 2, http://links.lww.com/QAI/A105). In contrast, the difference of CD8 T cell count between Hispanics and non-Hispanics disappeared when ORF65 serostatus was considered.
The results thus far indicated an association of CD4 T cell count, HIV load, or duration of HIV infection with ORF65 but not LANA serostatus. We examined effects of these factors on antibody detection in KSHV-infected patients by logistic regression adjusting for age and ethnicity (Table 2). HIV load had no effect on detection of latent or lytic antibodies. However, detection rate of latent antibodies was lower in those with CD4 T cells/mm3 less than 200 than greater than 200 (35% versus 67%; OR, 0.26; 95% CI, 0.11-0.61; P = 0.002), CD8 T cells/mm3 less than 400 than greater than 400 (28% versus 64%; OR, 0.22; 95% CI, 0.07-0.67; P = 0.007), and duration of HIV infection greater than 15 years than less than 15 years (45% versus 62%; OR, 0.42; 95% CI, 0.18-1.02; P = 0.057), although the latter was not statistically significant. Thus, lower CD4 and CD8 T cell counts impeded antibody responses to latent antigens. In contrast, lower CD4 T cell count (92% versus 71%; OR, 3.41; 95% CI, 0.93-12.45; P = 0.064) and longer duration of HIV infection (87% versus 73%; OR, 5.28; 95% CI, 1.50-18.59; P = 0.010) increased detection rates of lytic antibodies (Table 2).
The ORF65 serostatus may reflect KSHV lytic replication status. We examined the main and interaction effects of KSHV-associated risk factors on relative ORF65 antibody levels in ANY + patients (Table 3). HIV load, CD8 T cell count, or other coinfections had no effect on ORF65 antibody level. In contrast, ORF65 antibody level was higher in patients with duration of HIV infection greater than 15 than less than 15 years (adjusted difference mean OD [admOD] = 0.324; 95% CI, 0.16-0.46; P = 0.001) and with CD4 T cells/mm3 less than 200 than greater than 200 (admOD = 0.105; 95% CI, -0.01-0.19; P = 0.063), although the latter was not statistically significant. ORF65 antibody level was negatively correlated with CD4 T cell counts (r = 0.407; P ≤ 0.001) and positively with duration of HIV infection at a marginal level (r = 0.157; P = 0.065) but not correlated with CD8 T cell count (P = 0.827) nor with HIV load (P = 0.135) (see Figure 2, Supplemental Digital Content 3, http://links.lww.com/QAI/A106). Consistent with ORF65+ rate, Hispanics had higher ORF65 antibody levels than non-Hispanics (admOD = 0.111; 95% CI, 0.03-0.18; P = 0.012) (Table 3).
Analysis of risk factor interactions showed a lower CD4 T cell count as a strong factor for a higher ORF65 antibody level when adjusted for other factors (data not shown). Duration of HIV infection remained a factor for a higher ORF65 antibody level, whereas CD8 T cell count and HIV load showed no association. The association of Hispanic status with higher ORF65 antibody levels was not affected by CD8 T cell count, HIV load, and duration of HIV infection but was marginally influenced by CD4 T cell count (admOD = 0.074; 95% CI, -0.01-0.14; P = 0.071).
A serologic assay with one antigen may be insufficiently sensitive to identify all KSHV-infected patients. Indeed, inconsistencies were observed among assays based on single antigen.30,31 Cross-examination with multiple assays including both latent and lytic antigens may increase the sensitivity and specificity for identifying KSHV-infected patients.29,35 As expected, our LAN A, ORF65, and BOTH seropositivity rates are within the reported ranges; however, the ANY rate (36%) is at the higher estimates.2-6
We found an overall higher KSHV seropositivity rate among patients with lower CD4 T cell counts or higher HIV loads (Table 1). Both factors could influence immune surveillance and hence KSHV lytic replication and serostatus. Indeed, both factors were associated with lytic seropositivity. However, a higher ORF65 antibody level was only associated with a lower CD4 T cell count (Table 3). Furthermore, the association of HIV load with ORF65 seropositivity was marginally affected by CD4 T cell count (data not shown). Thus, immune status is likely a better predictor than HIV load for opportunistic diseases, confirming the observation that HIV load does not always predict immune status, including CD4 T cell count.36
In contrast to KSHV lytic antibodies, lower CD4 and CD8 T cell counts and longer duration of HIV infection affected detection of latent antibodies (Table 2). Whether this observation can be extended to all latent antigens remains unclear. A previous report has also shown dependence of detecting LANA antibodies on CD4 T cell counts.37 These findings explain why previous studies failed to observe an association of LANA seropositivity with CD4 T cell count and HIV load.4,11,15,38
In the early AIDS epidemic, patients rapidly progressed to KS after KSHV seroconversion with over half developing KS within 12 months.2,3,39 We found higher KSHV seropositivity rates and lytic antibody levels in patients with duration of HIV infection greater than 15 years than less than 15 years (Table 3). These associations were not confounded by other factors, indicating that longer duration of HIV infection is an independent predictor for KSHV seropositivity and higher lytic antibody levels. Of note, classic KS is commonly found in elderly men.1 Whereas HIV infection and resulting immunosuppression were dominant factors controlling KS development in early HIV epidemics, HAART has reduced their effects as manifested by the reduced KS incidence in the last decade.40 As patients live longer, other factors such as duration of HIV infection have emerged as cofactors.
We found higher ORF65+ rates and higher ORF65 antibody levels in Hispanics than in non-Hispanics (Tables 1 and 3). KSHV epidemiology in South Texas is distinct with a slightly higher seroprevalence in the general population than other US regions (15% versus less than 12%)34 and a unique spectrum of KSHV genotypes, including 75% K15M subtype and 50% K1C3/K15M mosaic genotype. These predominant genotypes are associated with Hispanics and an advanced KS stage,41 suggesting a viral factor might contribute to an increased risk and a more advanced KS stage. Nevertheless, association of Hispanics with ORF65 seropositivity, although not ORF65 antibody level, was confounded by other factors. Although Hispanics and non-Hispanics had a similar duration of HIV infection and HIV load suggesting their comparable treatments, Hispanics had lower CD4 and CD8 T cell counts than non-Hispanics (see Figure 1A, Supplemental Digital Content 2, http://links.lww.com/QAI/A105). Thus, genetic or environmental factors might contribute to worse HIV-induced immune deterioration resulting in higher risks for KSHV seropositivity and higher lytic antibody levels.
A limitation of this study is its cross-sectional nature. Our subjects were enrolled in a prospective cohort study; however, we lacked sufficient cumulative follow-up experience to elucidate the direct relationship between KSHV infection or lytic replication and incident KS. Although we used three referral clinics, our population might not be reflective of the general HIV population. Strengths include the diversity of the population with a high proportion of Hispanics and simultaneous examination of KSHV latent and lytic antibodies.
In summary, besides high HIV load and deteriorated immunity, extended duration of HIV infection, probably a result of HAART, increased the risk for KSHV seropositivity and lytic antibody level, and thus may contribute to a higher risk for developing KS. South Texas Hispanic patients with HIV appear at a higher risk for KS than other US regions. Results of this study should be considered for long-term management of HIV patients in the HAART era.
We thank Dr. Philip LoVerde for his constructive comments, Jodi A. Tullman, MS, RN, CCRC, and Robert A. Aakhus, BBA, MT, for their help in recruiting study subjects at the HIV Unit at San Antonio Military Medical Center, and technical helps of members of Dr. Gao's laboratory.
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Keywords:© 2011 Lippincott Williams & Wilkins, Inc.
KSHV; Kaposi's sarcoma; latent and lytic antibodies; risk factors; HIV/AIDS