Lymphoid tissue fibrosis is associated with impaired vaccine responses

Abstract

Vaccine responses vary by geographic location. We have previously described how HIV-associated inflammation leads to fibrosis of secondary lymph nodes (LNs) and T cell depletion. We hypothesized that other infections may cause LN inflammation and fibrosis, in a process similar to that seen in HIV infection, which may lead to T cell depletion and affect vaccine responses. We studied LNs of individuals from Kampala, Uganda, before and after yellow fever vaccination (YFV) and found fibrosis in LNs that was similar to that seen in HIV infection. We found blunted antibody responses to YFV that correlated to the amount of LN fibrosis and loss of T cells, including T follicular helper cells. These data suggest that LN fibrosis is not limited to HIV infection and may be associated with impaired immunologic responses to vaccines. This may have an impact on vaccine development, especially for infectious diseases prevalent in the developing world.

Keywords: Adaptive immunity; Bacterial vaccines; Fibrosis; Immunology; Vaccines.

Figure 1. Increased immune activation in HIV^– Ugandans.

Prevaccination plasma samples demonstrated elevated levels of TGF-β (A) and IL-6 (B) in a group from Uganda compared with a group from the U.S. LN sections stained for Ki67 also demonstrated increased immune activation when compared with LN tissues obtained from people in the U.S. (C). Representative sections of LN stained with Ki67 antibodies from an HIV negative person in Minnesota (D) and an HIV negative Ugandan (E) are shown. Scale bars indicate 100 μm and magnification is ×10.

Figure 2. Increased T cell zone fibrosis in people from Uganda.

A representative section of LNs stained with trichrome from a person from the U.S. (A) was compared with one from a person from Uganda (B). There was an increase in the amount of collagen (blue fibers) in the Ugandan sample. LN tissues from the Ugandan participants in Group 1 have a similar amount of collagen as LN tissues from HIV^– people from the U.S. in Group 2 (C). We see the expected inverse relationship between TZ collagen and the size of the resident CD4⁺ T cell population in the HIV^– Ugandans (D). Scale bar indicates 50 μm and magnification is ×20.

Figure 3. The fibroblastic reticular cell network (FRCn) is depleted in Ugandans.

We used QIA to identify TZ desmin in HIV^– people in the U.S. (Group 2, A) and people from Uganda (Group 1, B and C) and then used quantitative image analysis to compare the amount of desmin in the section to the size of the CD4⁺ T cell population in the LN (D), showing the significant and direct relationship. Scale bar indicates 100 μm and magnification is ×20.

Figure 4. Dermatopathic lymphadenopathy and CD4⁺ T cell depletion in HIV^– Ugandans.

H&E staining (A) of Ugandan LNs reveals prominent features of dermatopathic lymphadenitis, including sinus histiocytosis in the TZ (black arrows) and melanin in phagocytes (red arrow). CD20 staining to identify B cells (B, black arrow) shows an expanded TZ (red arrow) compressing B cell follicles (which are reduced in number) against the capsule. Scale bar indicates 200 μm and magnification is ×4.

Figure 5. Ki67 and CD20 analysis in LNs before and 2 weeks after yellow fever vaccination in Group 1.

There is no significant increase overall in the frequency of Ki67⁺ or B cells in the LNs after vaccination.

Figure 6. Yellow fever antibody titers.

Titers of neutralizing antibody titers from the Ugandan and U.S. groups are compared using a plaque reduction neutralization assay with a starting dilution of 1:20 (A), demonstrating that by week 2 all of the U.S. participants had detectable antibodies but only 5 of 20 people from Uganda did. In (B) we show the peak titer of the Ugandan participants at day 21 (week 3) and the decline through month 14. In (C) we show that measures of desmin in LNs correlate to peak antibody titer.

Figure 7. B cell follicles are diminished and there is a paucity of T follicular helper cells in B cell follicles in Ugandans.

This figure shows LN analysis from 3 different participants before vaccination and again at week 2 after vaccination. Participant 1996 has recognizable follicles before vaccination and formation of follicles after vaccination. The accumulation of PD1 staining cells within the secondary follicle (D) with green and blue staining cells in the secondary follicle (staining yellow) show an expected reaction to vaccination. Panel B shows participant 1682 with fewer, more poorly formed follicles at baseline and a lack of recognizable secondary follicles with vaccination. PD1 staining cells are not inside of the follicle structure. Participant 1688 has no recognizable follicles prior to vaccination and no response to vaccination. Scale bar indicates 20 μm.

Figure 8. Changes to plasma cytokines with yellow fever vaccination in groups 1 and 3.

Changes in measures of TGF-β and CXCL13 are in pg/ml and all other cytokines are changes in mean fluorescence intensity (MFI). Mean plasma values and P values for differences between groups and with yellow fever vaccine are shown in Table 2.